FOSSIL SHELLS OF THE SILURIAN AND DEVONIAN ROCKS. BY HENRY NETTELROTH. PART II. DESCRIPTION OF SPECIES. FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. COELENTERATA. SPONGIA. Genus Brachiospongia. Marsh. Described by Marsh in Am. Journal of Scie. and Arts., 2d series. Vol. 44, 1867—Etymology: brachium, an arm; spongia; a sponge. Brachiospongia digitata. OWEN Plate XXXV., figure 3, and Plate XXXVI., figures 1 and 3. Scyphia digitaia, Owen. First Ky. Geol. Rep., Vol. II., p. 111—1857. This fossil i s v ery peculiar, and very interesting; Prof. D. D. Owen, who described it in his Kentucky Report, placed it in the genus Scyphia of Schweigg, but its proper place is in the later established genus Brachiospongia of Marsh. It consists of a circular or elliptical central body, which is hollow, and has on its lower side an elliptical aperture occupying about one-third of the lower surface. This a perture i s s urrounded by a n e levated t hick brim, w hich r ises in t he specimen before me more than an inch and a quarter above the general surface; its greater diameter measures four and its smaller two inches and a quarter. From the circumference of t he cen tral body r adiate i n m y shell t welve l arge, cy lindrical, geniculated tubes, while in fossils seen by Prof. Owen he counted only from eight to e leven. T hese t ubes s tart f rom t he pe riphery w ith a dow nward di rection f or about a little more than an inch, where they make an abrupt turn of about ninety degrees u pwards, to t he extent o f m ore than t hree i nches. I f t he i nterspaces between the t ubes w ere c losed, t he f ossil w ould f orm a m edium sized ba sin or bowl, with an elevated center. The tubes are all of about the same size and shape; all have an aperture on top, which is different in shape; in some the opening is elliptical, w hile in o thers, i t extends to t he kne e; bu t there i s n o d oubt t hat, i n original specimens, t he ap erture w as limited t o the t op, and th e la teral enlargement of the 30 PALÆONTOLOGY OF KENTUCKY. opening is due to wear and rubbing in its fossil condition. The internal structure is destroyed, a nd o nly t he o utline or ge neral f orm pr eserved. The central bo dy measures six inches in diameter, while the circle, formed by the tops of the tubes, has a diameter of nine inches. Formation and Locality.—This interesting fossil is limited to one locality; it is found in the lower strata of the Cincinnati or Hudson River group, at Bright's Mill, on Benson Creek, a few miles west of Frankfort, Ky., where, altogether, not more than about a dozen fair specimens have been found, while fractional specimens are more numerous. MOLLUSCA. BRYOZOA. Genus Ptilodictya. Lonsdale. Ptilodictya, Lonsdale. Murch. Sil. Syst.—1839. Etymology: ptilon, a wing; dictyon, a net. The correct orthography would be Ptilodictyon. Fronds s imple or br anched, s pringing f rom a p ointed or wedge-shaped, s ub-- solid, and finely striated base or articulating process, which fitted loosely in the socket of the expanded and firmly attached base. The free portion of the zoarium is t wo-edged, with t he transverse o r cross s ection a cutely elliptical, with t he surface either smooth, montiferous, or marked by transverse ridges, and composed of t wo equal but d istinct s ides; each si de is provided with a delicate epithacal membrane, f rom w hich t he c ells rise to open on the two opp osite f aces of the frond. C ells q uadrate, r homboidal, or h exagonal, a nd a rranged i n l ongitudinal series, or in a quincuncial manner; pseudo-septa are frequently present; the walls are pi erced i n m any s pecies by connecting foramina. The interstitial cells are usually absent; but in the nodose species the summits of the monticules are often occupied b y s maller cells t han t he av erage. In t he robust s pecies t he t ubes a re crossed by diaphragms placed upon the same level in contiguous tubes. Ptilodictya hilli. JAMES. Plate XXXV., figures 1, 2, 4 and 5. Ptilodidya hilli, James. Cin. Journ. of Nat. Hist., Vol. V., pt. 3, plate 7, figure 7, no descpt.—1882. Zoarium d igitate, the n umber of prongs not k nown; t he s pecimen before m e shows one complete branch, which deflects from the original stem, just above the wedge-shaped articulating process, out of the sharp edge, and extending in the same plane with the main stem. On one of the broad sides of the main stem, and in its center, line, are two protuberances, the one opposite FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 31 the center line of t he deflecting branch, and the other about one-fourth of a n inch above i t, which a ppear t o be t he b uds of t wo ne w br anches, but w hose p ositions make it somewhat doubtful, inasmuch as those new stems would leave the plane of the t wo e xisting pr ongs. In similar s pecies, a s P . ramosa an d P . b riareus, the branches start always from the sharp edge, and I do not doubt that the same is the case with P. hilli. We may, therefore, assume, that very few branches are formed. This species is generally found i n more or less straight, thin strips, of different width, the cross sections of which are either acutely elliptical or elliptic-lanceolate. Both sides are entirely equal; they are most convex in their central line, from where they slope in a regular but gentle curve to the lateral margins, where the surfaces of both sides m eet a t a ve ry a cute a ngle. T he s urfaces of bot h sides a re c overed by transverse, sharply angular ridges, with interspaces of about twice their own width. Some of these plications cross the branches from one edge to the other in a straight line, rectangular w ith th e margin, the c ourse of ot hers is somewhat obl ique, a nd others again cross the surface only partly. These shorter ribs are always intercalated, and ne ver pr oduced by bi furcation. T he w hole z oarium i s c overed by c losely arranged rhomboidal c ells of a bout e qual s ize, t he w alls of w hich form ne arly straight lines, crossing each other obliquely. The largest specimen in my possession measures nearly four inches in length, by m ore than an inch in width; in its whole extent it does not show any branch; it has thirteen transverse ribs in the space of an inch. A smaller specimen measures one inch and three-eighths in length, by one-- fourth of an inch in width, with nineteen cross ribs in the space of an inch. Formation and Locality.—This species is n amed a fter Dr. O. O. Hi ll, formerly o f C incinnati, O hio, who first discovered it. It was afterwards found rather abundantly in the upper strata of the Hudson River group at Danville, Ky., by Prof. Linney, of the Kentucky Geological Survey. MOLLUSCA. BRACHIOPODA. Genus Crania. Retzius. Crania. Retzius. Schrift der Berliner Gesellschaft Nat. Freunde. 1781. Etymology: Kranion the upper part of the skull. Shell smooth or striated by radiating striae; umbo of the dorsal valve sub-central; umbo of the ventral valve sub-central, marginal or pr ominent and cap-like, with an obscure triangular area traversed by a central line. Shell usually attached to other shells or marine bodies. The large muscular impres- 32 PALÆONTOLOGY OF KENTUCKY. sions of the attached valve are sometimes convex, in other species, deeply excavated; those of the upper valve are usually convex. In C. tripartita of Münster, the nasal process divides the fixed valve into three cells. Some of the species are either entirely free or but slightly attached. Crania craniolaris is the type of the genus, which extends from the Lower Silurian to the present day. Crania bordeni. HALL AND WHITFIELD. Plate II., Fig. 14. Crania bordeni, H. & W. 24th Regent's Report, p. 187—1872. Crania bordeni, H. & W. 27th Regent's Report, pl. 9—1875. Shell depressed conical, about half as high as wide; beak sub-central, slightly nearer the anterior end. Surface marked by fine radiating striae, and somewhat strong lines of growth, giving a rugose character to surface, especially toward the margin. This species resembles Crania crenistria, from the Hamilton group of New York, but that species is more coarsely striated than our shell. Formation and Locality. Found in the rotten hornstone and in the cherty layers on top of the hydraulic limestone of the Devonian formation in Jefferson county, Kentucky, and in Clark county, Indiana. The quarries for hydraulic cement rock at Watson's Station, on the Ohio and Mississippi Railroad, furnished the fine specimen of Modiomorpha concentrica, to which two fine individuals of Crania bordeni are attached. Genus Discina. Lamarck. Discina. Lamarck. Hist. Nat. des Animaux sans vertebres. 1819. Etymology: discus, a flat round plate; the termination inus implying resemblance.