340 



GEOLOGICAL SURVEY OF TEXAS. 



is about one-fourth of a volution in length and still incomplete. The speci- 

 men is much narrowed by compression, and making due allowance for this 

 the abdomen is slightly broader than the dorsum, measuring through the um- 

 bilical shoulders, and it has been so represented in the drawing. The amount 

 of involution is slight, the whorls being in contact only along the surface of 

 the slightly convex abdomen, and there is consequently only a shallow im- 

 pressed zone in the dorsal surface of each whorl. Nevertheless the increase 

 by growth in the dorso-abdominal diameter of the whorl is evidently rapid. 



Specimens of this and some other species were received through the 

 courtesy of Captain George E. Pond, of Fort Riley, Kansas. 



The front view (Fig 39) is in large part restored from a much compressed 

 specimen. 



Its nearest ally occurs in the Carboniferous in Russia. It differs from 

 Metacoceras [Nautilus) Tschernyschewi, Tzwetaev,* in having somewhat broader 

 sides and a narrower abdomen at the same age, and fewer tubercles. These 

 also are elongated longitudinally, whereas in Tschernyschewi they are elon- 

 gated transversely forming a series of rib-like folds. 



Metacoceras inconspicuum, n. s. 



Loc. Kansas. 



Coll. R. Hay. 



Figs. 40, 41, natural size. 



This cast has an aspect which 

 at first sight leads one to think 

 it is a species of Tainoceras, but 

 the abdominal sutures are defi- 

 cient in the pair of saddles dis- 

 tinguishing that genus, and 

 there are no lines of abdominal 

 tubercles. The whorl increases 

 in abdomino-dorsal diameters 

 faster than Metacocoras cavati- 

 formis, but not in the transverse 

 diameters; the whorl is conse- 

 quently more compressed. The H^ 

 umbilical shoulders are not so 

 angular as in that species, and 

 the sides broader and less con- 

 vergent outwards, and the tu- 

 bercles upon the outer border of 



*Ceph. du Calc. Carbonifere de la Russie Centrale, Mem. du Com. Geol., V, No. 3, PI. 2, 

 Figs. 7-9. 





