SHUMARD—CRETACEOUS FOSSILS. 593 
points on either side, the terminal ones being the larger and 
trifurcate; dorsal saddle double the width, but shorter than 
the dorsal lobe, divided into two unequal parts by a slender 
digitate auxiliary lobe; superior lateral lobe shorter and nar- 
rower than the dorsal lobe, ornamented with five small 
branches on each side, the terminal ones trifid, and the 
others simple or bifid; inferior lateral lobe narrow, much 
smaller than the superior, having eight. branches, the termi- 
nal ones bearing two or three points. 
In young individuals, the dorsum is more flattened than in 
mature shells, the sides slightly converge towards the ventral 
margin, and occasionally we find small nodes in the intervals 
between the larger ones of the dorsal margin. 
The 4. Meekianus is founded merely upon fragments of 
the exterior volution, which, however, show the form of the 
lobes of the septe very perfectly, so that there is no danger 
of confounding it with any other American species. 
idth and thickness of last volution, two inches. 
Form. and Locality—Occurs with the preceding species 
hear Post-Oak Creek, Grayson County. Dedicated to the 
able Paleontol gist and Geologist, F. B. Meek, Esq., of 
Washington, D. ©. 
A. GRAYSONENSIS, 0. sp. 
of them extending to the dorsal carina, being abruptly bent 
forward, and most prominent on the dorso-lateral margin. 
Thave before me a number of examples of this species, but 
none of them show the form of the chambers. 
ameter, 1.43 inches; width of last volution at aperture, 
18 shell is very nearly related to A. percarinatus, of Hall 
P| K (Mem. Amer, Acad. Arts & Sci., Vol. V., p. 396, 
a lv., Fig. 2 a—c.), from which it may be distinguished by 
b Waved-edge and less prominent dorsal carina. The Ne- 
— shell has also a greater number of ribs. * 
orm. and Locality—Occurs in septarie, embedded in the 
Lower Cretaceous Marls in Hasits Coutts, near Lowell’s 
