2Y6 DESCRIPTION OF A COLLECTION OF FOSSILS, 



from all the known species of the group. The inferior lateral lobe is entirely 

 unlike that of A. cordatus, as is all the remainder of the septum to the suture ; 

 and the resemblances in the dorsal and superior lateral lobes are very remote. 

 From the North American A. cordiformis, Meek and Hayden, the differences of 

 the septum are still greater; besides which, the only known specimen of that 

 species is strongly costate on the surface, and much more compressed, although 

 these external characters might be only individual in character. Prof. Hyatt, to 

 whom I sent the specimen figured, returned it to me labelled cordatus, but I 

 suspect he did not compare the septa of the two forms. 



GASTEROPODA. 



PERISSOLAX, Gabb. 



P. TROCHOIDES, Tl. S., PL 39, fig. 4. 



Shell trochiform, spire low; body whorl convexly flattened above and sloping; 

 below, it slopes rapidly inwards; aperture broad, irregularly rounded subquadrate; 



canal produced. 



Locality. Hacienda of Macanga ; Pro v. of Pataz. Cretaceous. 



Remarks. I have ventured to describe this species from a couple of casts, 

 retaining all the parts except the long slender canal, characteristic of the genus. 

 They retain no part of the shell, but show traces on the broadest part of the whorls 

 of three or four revolving ribs. This species is allied to P. longirostris, d'Orb., 

 sp. {Pyrula), Amer. Merid., p. 119, PI. 12, fig. 13; Voy. Astrolabe and Zelee, PI. 4, 

 f. 30 ; but in that species, as well as in P. Homhroniana, the body whorl is broader 

 and rounder, while in ours the greatest width is near the upper angle. 



Indet. Several other casts from the same locality occur in the collection. They 

 are from a buff-colored limestone, but none show specific characters; and, in most, 

 even the means of determining the genus is lost. 



GYRODES, Con. 



G. CONTRAOTA, n. s., PL 39, fig. 5, 5a. 



Shell small, subglobose, oblique ; spire low, whorls five, flattened and faintly 

 channelled above ; suture distinct and bordered by a slight thickening of the suc- 

 ceeding whorl ; body whorl most convex in the middle, contracted in advance ; 

 umbiUcus open, but unusually narrow; aperture nearly semicircular, with the 

 inner margin vertical, and subangulated above by the flattened top of the whorl ; 

 lips simple. Surface marked by very oblique lines of growth, which are most 



