TRIASSIC FOSSILS. 25 



This shell is closely allied to A. scaphitiformis, Hauer ; but the umbilicus seems 

 to be larger ; and the septum, which is of the same general style, is much more 

 complex, especially in the dorsal and superior lateral lobes. 



A. AUSSEANUS, Hauer. 



Plate 3, Figs. 16 and 17. 



SHELL subglobose ; whorls deeply enveloping, increasing very 

 gradually in size. Umbilicus small, profound. Surface smooth 

 or striate by indistinct lines of growth. Cast marked at intervals 

 of one-fourth of a volution by a deep groove, caused by a thicken 

 ing of the shell. These constrictions bend slightly backwards at 

 their origin, near the umbilicus, then arch forward on the side 

 of the whorl and pass straight across, or curve a little backwards 

 again on crossing the dorsum. This last character is not always 

 constant. I have seen several specimens where it was entirely 

 absent, and others in which it is but faintly exhibited. Aperture 

 compressed crescentic, very deeply emarginate. 



Septum : Dorsal lobe divided for half its length into two branches, 

 each of which is subdivided into three smaller ones ; two smaller 

 spurs above the branches; dorsal saddle about as wide as the 

 lobe, and trilobate at the end; superior lateral lobe divided into 

 three branches at the end, with two above on each side, all vari 

 ously toothed; superior lateral saddle like the dorsal saddle ; lateral 

 lobe like the preceding one, except that it has but two terminal 

 branches, each of which is bifurcate; lateral saddle like the 

 others, but smaller ; inferior lateral lobe like the superior lateral, 

 only differing in being smaller. There are, besides these, two 

 smaller lobes and saddles. 



Dimensions : Diameter, 2.45 inches. Height of aperture at the 

 dorsum, .55 inch. Width of aperture, 1.5 inch. 



This shell is so nearly like Hauer's figure that I have referred it to the same 

 species. It is more compressed laterally, and there seems to be a little difference 

 in the lateral lobes of the two forms ; but these points are not of enough im 

 portance to warrant a separation. 



PAL. VOL. I. 4 



