i DECAPOD CRUSTACEANS FROM THE CRETACEOUS OF TEXAS H. B. Stenzel In the Tertiary and Cretaceous strata partly by the staff of the Bureau of Eco- of Texas, decapod crustaceans are not nomic Geology. The writer is indebted uncommon, at least at some localities. to the collectors for some of the finest There are even a few localities where specimens. Proper credit is given in the these decapod crustaceans are amazingly text to those who have helped to gather abundant. California Crossing in Dallas the material. The writer wishes to express County is one of these localities. The his appreciation of their efforts and abundance and fine preservation of mate- generosity. rial, from such localities present a chal- lenge to the paleontologist, and this chal- NOTES ON THE COMPARATIVE ANATOMY lenge is ' strengthened by the importance OF THE MACRUROUS DECAPOD v of much of the nj$iterial. V CRUSTACEANS So few fossil decapod s^i'ustaceans have One of the clearly outstanding features been collected etnd described in- this coun- of highly developed animals is the eye. try that nearly every", new"' locality also Among many of these animals it is the yields new species, ajjd man*' of the eye which is the chief sense v organ. Its genera are new tp fiiis, country. In addi- proper function as an organ of vision tion, the knowlpd^' qf decapod crusta- aids the animal in protection from at- ceans here and abroad is very incomplete 1 tack, in quest of food, in search for s« tjiat some of the finds result in, signifi mates, and in other essential functions. ant Extensions of- the straiigraph'ic range Therefore, it is important that the eye the genera. - be protected from any injury in fight or is fortunate that some of the species, by accident. In the mammals this pro- notaAly Ceno manocar cinus vanstraclehi tection is afforded by bony structures StenzlL are represented by copious mate- surrounding the orbit of the eye. In those rial, wkich makes -it possible to d'efecribe mammals which depend very mucb on the f nearly ai^ parts of the animal--carapace, use of the eye — man is one of them — the abdomen, arid . appendages.* Such fully orbit is protected by the bones of thfe nose, described species are very,,,much needed eyebrows, and cheeks. These bones en- as a firm standard around which may be circle and surmount the orbit, so that the grouped the less known sptecies, that' is, eye is freely movable and yet surrounded described from isoiated fragments. by hard ridges. In such fully described species 'are the /. The same problem exists in crusta- means of elticicZ ( phylogenetic rela- tions as, for instance, the relations be- ceans. The eye must be protected in those- tween Necrocar cinus and Cenomanocar- crustaceans in which the eye is of para- cinus. Also these fully known species mount importance as a sense organ. In may be used to correct misidentifications the crustaceans, as in the mammals, this caused by insufficient material in other protection is accomplished by hard ridges. related species. A case in point is the Naturally, the ridges are not composed recognition of the true nature of Rani- of bones as in the mammals, because nella (?) armata Rathbun. Or the fully crustaceans do not have an interior bony known species may be used to improve • skeleton. Among the crustaceans the the understanding of related but less ridges are parts of the exoskeleton. For copious material. A case of this sort is example, the eye of a lobster (see text the right manus of Upogebia gamma fig. 1) is surrounded by 11 protective (Rathbun) which was originally described spines. Thes'e spines form an oblong de- as the left manus. fense ring around the orbit, giving the These fossil crustaceans were collected eye the much needed protection from partly by local enthusiastic collectors and enemy or accident. t A } 402 The University of/ Texas Publication No. 4401 t .. — /AV-O-" Tvv IV J'* \\ - N""— —__ \ Fig. 1. The protection of the eye in an Astacuran crustacean, the American lobster, Homarus americanus H. Milne-Edwards, 2/3 of natural size. For explanation of the symbols of the spines, see the text. Abbreviations of grooves 6n th6 carapace: a, branchio-cardiac; b, antennar; bi, hepatic; c, postcervical; d, gastro-orbital; e-ei, cervical; m, marginal. The position of the eminence omega is indicated by the Greek letter. These protective circum-orbital spines ogous structures in nearly all macrurous are distributed in Homarus americanus H. crustaceans. Milne-Edwards as follows: In order that an unequivocal terminol- ogy may be used, these spines were la- 2 median spines on ventral surface of rostrum 1 (unpaired) belled by Boas with letters or numbers^ 1 tip of rostrum (unpaired) His terminology has been used to advai 3 spines at lateral edges of rostrum (paired) tage by other paleontologists and is /re- 3 spines on the carapace (paired) tained here. In addition, a set of vi 1 spine on distal end of exopodital scale of is used for the spines. £ antenna (paired) 1 spine on distal end of second protopodite Terminology of the circum-orbital spines of segment of antenna (paired) macrurous crustacea^is. The two orbits together have 19 spines, Boas This paper because the 2 median spines on the ven- r tip spine of rostrum tral surface and the tip spine of the ros- 1 first lateral rostral spine ] on trum are unpaired. The 2 median spines 2 second lateral rostral spine }• rostral . of the ventral surface of the rostrum are 3 third lateral rostral spine J ridgp>" present in Homarus americanus H. Milne- a supra-orbital spine 1 ' Edwards but are absent in Homarus vul- P sub-orbital spine on garis H. Milne-Edwards and in fossil 7 antennar spine J carapace species of the genus. Therefore, they will In many instances the spines are devel- henceforth be omitted from consideration. oped from longitudinal ridges. The ros- The spines on the segments of the an- tral spines are portions of the two ros- tenna are rarely preserved in fossil speci- tral ridges (p), which extend along the mens. Thus are left the following spines: lateral margins of the rostrum and unite in the tip spine. The supra-orbital, sub- 1 tip of rostrum, unpaired (r) 3 lateral spines of rostrum, paired (1, 2, 3) orbital, and antennar spines are the an- 3 spines on carapace, paired (a, P, y) terior ends of more or less well-developed, longitudinal ridges or keels, which bear These 13 spines are preserved and recog- the terms supra-orbital, sub-orbital, and nizable in many fossil species of Homarus. antennar ridges or keels respectively. In However, their importance lies not only addition, there may be a median ridge in their occurrence in this one genus but iBoas, J. E. V., Studier over Decapodernes Slaegtskabs- also in their occurrence in many genera. forhold: K. danske vidensk. selsk. skr., 6 raekke, naturvid. In other words, it is possible to find homol- jnath. Afd„ vol. 1, art. 2, pp. 23-210, pis. 1-7, 1880. / ^ Decapod Crustaceans from, Cretaceous of Texas 403 (/A) alpng the midline of the rostrum small or wanting (except in Palinurellus and the carapace. and the Glypheidea), the protection of the It has been mentioned above that the eyes is taken over by the supra-orbital importance of these structures lies not spines (a), and the eyes are far apart. only in their occurrence in the genus In addition, the depression of the cara- Homarus but also in their occurrence pace has put the antennar spines (y) into in many genera. The diagram (fig. 1) a much more prominent and exposed po- may serve to indicate the shape and ar- sition, namely, at the antero-lateral cor- rangement of these features in the tribe ner of the carapace. Such an exposed Astacura. position necessitated the enlarging of The tribe Palinura differs from the these spines. Thus, the Palinura (with Astacura in several features, among which some exceptions) have as the most promi- tfye shape of the carapace is of concern nent features of the frontal part of the to the present study. The carapace of carapace th>e supra-orbital (a) and the the Astacura is subcylindrical, whereas antennar (y) spines, between which the the carapace of the Palinura is depressed. eyes find adequate protection. The dia- The shape of the carapace determines the gram (fig. 2) shows the protection of the relative position of the eyes or rather the eye in Astacodes as an example of the relative distance from one eye to the Palinura. other. If the carapace is subcylindrical, as in the Astacura, the eyes are relatively close together; if, on the other hand, the carapace is depressed, as in the Palinura, the eyes are comparatively far apart. If the eyes are close together they can be pro- tected very effectively by a prominent rostrum projecting halfway between them. On the other hand, if the eyes are far apart they can not be protected effectively by a median rostrum unless the rostrum becomes unusually broad, in which case the rostrum may interfere with the essen- tial function of the eyes. Therefore, if the eyes of the Palinura were to be pro- tected, there was the choice of either broadening the median rostrum to fit the enlarged distance between the eyes or let- ting another organ take over their protec- tion. In the latter case the rostrum would lose its prime function, that is, the role Fig. 2. The protection of the eye in a Pali- of protector of the eyes, and become re- nuran crustacean, the fossil spiny lobster Asta- duced in size or even suppressed.