NATURAL SCIENCES OF PHILADELPHIA. 263 



third of a volution. It indicates a subglobose form for the entire shell, and 

 shows that the umbilicus was deep, with rather abrupt walls, and about as 

 broad as three fourths the do; so-ventral diameter of the body whorl at the 

 aperture. From the curve, and rapid increase in size of the outer chamber, 

 it is evident there could not have been more than two and a half volution9, 

 which are rather broadly rounded over the dorsum and sides, to the margins 

 of the umbilicus, into which the sides round rather abruptly. Towards the 

 aperture, the steep, somewhat flattened inner side of the volution forming the 

 walls of the umbilicus, meets the lateral margins, so as to form a pinched out 

 prominence, that must have imparted a p-culiar angularity to the inner mar- 

 gin of the aperture on each side. Just outside of this prominence, the ventro- 

 lateral sides of the outer whorl at the aperture are a little flattened. The 

 aperture is one-fourth wider than its dorso-ventral diameter, and forms about 

 three-fourths of a circle, being deeply rounded on the dorsal side, much flat- 

 tened within, and angular or apparently abruptly sinuous at each inner lateral 

 margin. These angles at the inner lateral margins, seem even to have pro- 

 jected out somewhat, as in the recent Argonauta gondola, of Adams, though 

 not to the same extent. The lip is rather deeply sinuous at the middle of the 

 dorsal side. The septa were moderately concave, and slightly arched back- 

 wards on each side. (Siphon and surface unknown). 



Greatest diameter of the shell, about 3 75 inches ; greatest breadth (at the 

 inner side of aperture), 2.65 inches. 



As we have not seen the siphon of this species, we are not sure that it be- 

 longs to the group Cnjptoceras, but from its analogy to the species just de- 

 scribed under the name capax, which shows apparently a dorsal siphon, we 

 are led to infer that it probably possesses the same character. It differs from 

 that shell, however, in having its body whorl less rapidly expanding, and 

 without a depression along the inner side forthe reception of the inner whorls. 



Named in honor of Prof. Joseph Leidy, of Philadelphia, Pa. 



Locality and position. Warsaw, Illinois. Keokuk division of the Subcar- 

 boniferous Series. 



Genus TROCHOCERAS, Barrande, 1847. 

 Trochoceras ? Baeri, M. & W. 



Shell subdiscoidal, consisting of about two or three rather rapidly enlarging 

 volutions, which are more broadly rounded ou the outer surface than on each 

 side, and about one-fourth wider transversely than their dorso-ventral diame- 

 ter ; each inner whorl slightly impressing the inner side of the succeeding 

 turn. Umbilicus a little more than half the dorso-ventral diameter of the 

 outer volution, and showing all the inner volutions. Spire apparently scarcely 

 rising above the upper surface of the last turn. Septa rather distinctly con- 

 cave on the side facing the aperture, separated on the outer side of the whorls, 

 at a point where the dorso-lateral diameter is about 1*25 inches, by spaces 

 measuring - 35 inches all showing a very slight backward jurve on the 

 rounded periphery, and passing nearly straight across each side. Surface, 

 siphon, and non-septate portion of the shell unknown. 



Greatest breadth of the septate part of the shell, 5 inches ; height, (estima- 

 ted) about 2-50 inches. Dorso-ventral diameter of the volutions, increasing 

 about three-fold each turn. 



The specimen from which this description was drawn up is defective on one 

 side, so that it is not easy to determine whether or not its whorls are coiled 

 in the same plane, though they have the appearance of being somewhat 

 oblique, and hence we have placed it provisionally in the genus Trochoceras. 

 Should it be found, however, when more nearly entire specimens can be ex- 

 amined, that its whorls are coiled all upon the same plane, it would belong 

 either to the genus Lituites or Nautilus, and hence its name would becoma 

 Lituites Baeri, or Nautilus Baeri. 



1865.1 



