48 PROCEEDINGS OF THE ACADEMY OF 



the same as Cryptoceras of D'Orbigny, published in 1850. This change of name 

 becomes necessary, however, because Dr. Barrande had used the name Crypto- 

 ceras for another widely distinct group of Cephalopoda in 1846. It is true he 

 has since changed the name of his genus to Ascoceras, for the reason that La- 

 treille had applied the name Cryptocerus to a genus of Hymenoptera in 1804. 

 But if Latreille's name Cryptocerus is not considered sufficiently distinct, on 

 account of its different termination, from Cryptoceras (which we should think 

 is the case), it would, for the same reason, of course, be equally necessary to 

 change the name of D'Orbigny's group. On the other hand, if we regard La- 

 treille's name as being distinct enough to permit D'Orbigny's name to stand 

 also, or if Latreille's genus is not a valid one, in either case Dr. Barrande's 

 original name Cryptoceras would have to be retained for his genus, and, as it 

 has priority of date, it would still become necessary to find another name for 

 the group described by D'Orbigny. 



The type of D'Orbigny's group was Nautilus dorsalis of Phillips, only known, 

 we believe, from a mere fragment, showing the siphuncle to be marginal, or 

 on the outer side of the curve, as in Ammonites.* In this country we already 

 know several Carboniferous species that agree with D'Orbigny's type in the 

 character or position of the siphuncle, and we find in all of these another re- 

 markable peculiarity of the lip on each side. That is, it is drawn so as to 

 form a kind of little canal, or spout-like channel, much as we see va.Argona.uta 

 gondola, Adams. A good example of one of these shells is figured and described 

 by Dr. White and Prof. St. John, under the name Nautilus (Cryptoceras) Sprin- 

 geri, in vol. i, p. 124, of the Transactions of the Chicago Academy of Sciences 

 for 1867 ; and this may be regarded as the type of the group. It also includes 

 our N. (Cryptoceras) Leidyi, N. (Crypt.) capaz, and the species described below, 

 with possibly our N. (Crypt.) Rockfordensis. 



The mere fact that these shells have the siphuncle marginal, as in Ammoni- 

 tes, would perhaps not alone be a sufficient reason for placing them in a sepa- 

 rate group from the typical Nautili, since the siphuncle occupies various po- 

 sitions in the different fossil species of the latter. But when we take into 

 consideration the additional fact that the marginal position of the siphuncle 

 in these shells is always accompanied by the peculiar character of the lip we 

 have described, it becomes of more importance. 



Nautilus (Solknochilus) collectus, M. and W. 



Shell thin, attaining a moderate size, slightly compressed or subglobose in 

 general form ; umbilicus rather small, but deep, perforated, and provided 

 with very abrupt walls, particularly near the aperture. Volutions about one 

 and a half, increasing rapidly in size, and a little wider transversely than their 

 dorso-ventral diameter ; moderately embracing, with a subquadrangular sec- 

 tion, the angles being rounded, and the lateral and outer or ventral surfaces 

 more or less flattened. Septa moderately concave, distant about one-fourth 

 the transverse diameter of the volutions at the point of measurement, and 

 showing a slight backward curve in crossing the sides and periphery ; aper- 

 ture large, and, as near as can be determined from the specimens, with a sub- 

 quadrangular or subcircular outline, more or less sinuous on the inner side 

 for the reception of the small inner turn ; siphuncle small. Surface smooth, 

 or only showing small lines of growth. 



Greatest diameter of a small specimen, with body chamber broken away, 

 1-70 inch ; transverse diameter of same, about 1-25 inch. 



As in other species of this group, the small siphuncle is so very nearly in 

 contact with the ventral, or outer side, that in casts with the shell removed 

 it often gives the appearance of a very narrow, deep lobe along the middle of 

 that side. It is easy to see, however, that this appearance is merely produced 



* M. Chenu figures on p. 72, vol. i, of his Manual of Conchology, under tho name Crypto- 

 ceras Bowerbahkit, Sowerby, a shell certainly not belonging to D'Orbigny's group as he un- 

 derstood it, but, if correctly figured, belonging to the Ammmitidx. 



[April, 



