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New Information on Homalonotus Trentonensis1 BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 41. PP. 341-350, PLS. 5-6 JUNE 30. 1930 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY NEW INFORMATION ON HOMALONOTUS TRENTONENSIS1 BY LAWRENCE WHITCOMB (Read before the Paleontological Society December 26,1929) 2 CONTENTS Page Introduction........................................................................................................................ 341 History.................................................................................................................................. 342 Taxonomy............................................................................................................................ 344 Description.......................................................................................................................... 345 Cranidium................................................................................................................... 345 Free cheek.............................................................................................. .................... 345 Hypostome.................................................................................................................. 345 Thorax.......................................................................................................................... 346 Pygidium..................................................................................................................... 346 Size................................................................................................................................ 346 Locomotion.......................................................................................................................... 346 Geographic distribution.................................................................................................... 347 Stratigraphie range..................................... ................................................................... 347 Correlation........................................................................................................................... 348 Acknowledgments............................................................................................................... 349 Explanation of plates........................................................................................................ 350 I ntroduction While collecting from the lower “Trenton” limestone, called the Salona formation by Professor Field3 in 1919, at the type locality, Salona, Clinton County, central Pennsylvania, in the summer of 1928, I obtained a large number of specimens of the trilobite described by Simpson4 forty years ago as Homalonotus trentonensis. Among the many dissociated parts were free checks and hypostomes, which had never been described, and one complete articulated cranidium, thorax, and pygidium. 1 Manuscript received by the Secretary of the Geological Society December 26, 1929. 2 An abstract of this paper was published in the Proceedings of the Paleontological Society for 1929 (Bull. Geol. Soc. of Am., vol. 41, p. 197, 1930). 8 R. M. Field : The Middle Ordovician of Central and South-Central Pennsylvania. Amer. Jour. Sci., vol. 48, Dec., 1919, pp. 403-428. 4 G. B. Simpson : New species of fossils from the Clinton, Lower Helderberg, Che­ mung and Waverly groups, found in the Collections of the Geological Survey of Penn­ sylvania. Trans. Amer. Philos. Soc., new ser., vol. 16, 1890, p. 460, flg. 31. (341) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/41/2/341/3430147/BUL41_2-0341.pdf by guest on 29 September 2021 342 LAWRENCE WHITCOMB----HOMALONOTUS TRENTONENSIS Homalonotus trentonensis is of particular interest because it is the oldest Homalonotid known in North America. Its stratigraphic and geographic range is limited, and it appears to be closely related to one of the Ordovician species found in Wales. It is the purpose of this paper to review the history of the species, to give a fuller and more accurate description of it in the light of this more complete information, and to compare it with its Welsh allies. H istory Simpson’s paper establishing the species Homalonotus trentonensis first appeared in separate form, bearing the date 1889, and was included in the volume of the Transactions of the American Philosophical Society cited. The paper included figures of the eranidia and two pygidia here considered, and contained the following statement: “The figures represent a few of the many specimens in the State collection, found by Mr. C. E. Hall in strata of the Trenton group cropping out Just above the milldam at Reedsville, in Mifflin County, Pennsylvania.” The species is listed in the “Dictionary of Fossils”5 of the Second Survey of Pennsylvania as follows: "Homalonotus trentonensis, Simp­ son. New species. For figures and localities, see the Appendix.” This appendix was never published. Under the authority of an act of the legislature of April 4, 1883, the collections of the Second Survey wer placed in the custody of the Acad­ emy of Natural Sciences of Philadelphia, where they are now preserved. In going through these collections, I was able to pick out the original cotypes, which have now been marked as such. The “Museum Catalogue”6 shows that the cotypes were not all col­ lected by Mr. C. E. Hall, as was stated by Simpson, although they were all obtained at the same locality. Of the specimens figured by Simpson, numbers 1, 2, and 4 were collected by W. A. Fellows in September, 1875. The specimens collected by A. Hale and C. E. Hall in May, 1875, and numbers 1, 2, and 4 were colected by H. Hale and C. E. Hall in May, 1875, and numbers 3, 5, and 6 were collected by W. A. Fellows in Sep­ tember, 1875. The specimens collected by Hale and Hall bear the field number 201; those collected by Fellows bear the number 204. Many of the paper labels that were pasted on the specimens have come off, so that it is now impossible to tell exactly what numbers were assigned to the types. Three type specimens, however, are known: Number 1 is 201-30, num­ ber 4 is 201-35, and numbers 5 and 6 are 204-5. 5 J. P. Lesley : Dictionary of Fossils, Pennsylvania Second Geol. Survey, 1889, T-4, vol. 1, p. 289. 9 C. E. H a ll: Museum Catalogue, Pennsylvania Second Geol. Survey, 1889, 000, vol. 3, pp. 170, 179. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/41/2/341/3430147/BUL41_2-0341.pdf by guest on 29 September 2021 HISTORY 343 According to the table in Merrill’s “Contributions to a History of American State Geological and Natural History Surveys,” 7 Fellows worked for the Pennsylvania Survey only in 1878 and 1879. His collec­ tions were probably made privately and acquired by the Survey, or a mistake has been made in the record of the date of their collection. Plaster casts of numbers 1, 4, and 5 of the cotypes are deposited in the New York State Museum at Albany. These casts bear the catalogue numbers 4495, 4496, 4497. The next reference to the species seems to have been made in 1903, when Dr. G. L. Collie 8 presented, at a meeting of the Geological Society of America, a paper on the “Ordovician Section Near Beliefonte, Penn­ sylvania.” In this paper Dr. Collie used the subgenerie name, Brong- niartia, which Salter9 had proposed in his revision of the genus Homa- lonotus. The species was figured anew, and for the first time part of the thorax was shown. The plesiotypes, a cranidium and a pygidium with ten thoracic segments attached, were collected from what he considered the basal zone of the Trenton at Bellefonte. In this paper, we get the first information about the associated fauna and a rough delimitation of the stratigraphic range of the species. Dr. Collie’s plesiotypes are now deposited in the Peabody Museum at Yale University under the number 7449. In 1919 Professor Field10 stated that he had found this species in many sections of the lower “Trenton” limestone in central Pennsylvania. He called it Brongniartella trentonensis, following the classification of F. R. C. Reed,11 and listed it as one of the characteristic fossils of his Salona formation, which he stated appeared to contain also an un­ described species of Brongniartella. I have studied Professor Field’s unpublished illustration and description12 of this species, which he called B. collianus, and believe that the specimens on which it was based are probably actually referable to B. trentonensis, and that Professor Field was misled by apparent differences which were'due solely to individual variations and to differences in preservation. 7 G. P. M errill: Bull. U. S. Nat. Mus., No. 109, 1920, p. 445. 8 G. L, Collie: Ordovician section near Bellefonte, Pennsylvania. Bull. Geol. Soe. Amer., vol. 14, 1903, pp. 407-420, figs. 1-2. 8 J. W. Salter: A monograph of tie British trilobites from the Cambrian, Silurian, and Devonian formations. The Paleontographical Society, London, 1865, pp. 104-105. “ Op. Cit. 11F. R. C. Eeed: Geol. Mag. new ser., decade 6, vol. 5, 1918, pp. 263-276 and 314- 327. 12 R. M. Field : Unpublished thesis, Harvard University Library. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/41/2/341/3430147/BUL41_2-0341.pdf by guest on 29 September 2021 344 LAWRENCE WHITCOMB---- HOMALONOTUS TRENTONENSIS T a x o n o m y Since 1825, when König13 chose the species hnighti as the genotype of Homalonotus, there has been a tendency to place an increasingly large number of species in that genus. By 1865, these species became
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