Hyatt.] 366 [January 20, 



course be fully described from such small collections, but the Lower 

 and Middle Lias are shown to be present, and the- difference in the 

 matrices of the specimens indicate still more minute subdivisions. 

 The penological pecularities of the specimens of Perispminctes 

 anceps and Steplianoceras macrocephalum also indicate minor sub- 

 divisions in the Upper Oolites, but these cannot be characterized 

 upon such slender data. 

 Arnioceras ceras ? Agassiz. 



1. Under this head I am obliged to assemble several very interest- 

 ing specimens, whose affinities cannot be positively determined without 

 more evidence. One specimen, about three inches in diameter, is the 

 cast of a crushed shell with straight or nearly straight ribs, quite 

 prominent and closely set. Older specimens show a set of bent ribs 

 with prominent keel, and narrow abdomen. The young are distinctly 

 ribbed at a very early period, and* but for this might be taken for 

 any of several species, viz., Arnioceras ceras or Bodleyi, Aster ocer as 

 Turncri (the English form, not the German). The old-age whorls in 

 the same block have an aspect like that of the full-grown Grammoce- 

 ras strialulum of the radians group. These specimens, though from 

 the same locality as the specimens of this species described below, 

 nevertheless occur in a matrix of argillaceous rock of compact struc- 

 ture with a pinkish color, which does not show the slightest efferves- 

 cence with strong acid. 



Loc, Jpishguanuna, Northern Peru. 



2. A large specimen from the same locality, but imbedded in a 

 soft, thin bedded, ferruginous, argillaceous rock of a dark brown color, 

 although much mutilated, shows similar characteristics and exhibits 

 the form of the whorl better. This shows that the species is prob- 

 ably very closely allied if not identical with Arnioceras ceras. The 

 ribs run up straight until level with the abdomen, and then assume 

 the abrupt termination so characteristic of this whole group. The 

 septa also, which are visible on this specimen, have the peculiar sim- 

 ple sutures of this genus with the pointed simple minor lobes and 

 cells penetrating the edges of the larger ones, the deep superior lat- 

 eral lobes and shallow inferior laterals, with no auxiliary lobes 

 appearing on the sides. 



The same form is in Europe characteristic of the Lower Lias, 

 occurring in great numbers at Semur. 



3. Another specimen also from this dark brown rock, fully agrees 

 with no species with which I am acquainted. It resembles somewhat 





