LOWEE CARBONIFEROUS FOSSILS. 567 



be possible to effect this scientifically by the use of constant characters 

 seems probable. Just what characters will assume such import, a detailed 

 critical study of the genus will develop. Therefore, I have ventured to 

 recognize certain types in the Yellowstone National Park collections which 

 I feel confident to be distinct from CI, roissyi of Leveille. Whether these 

 will ultimately prove tenable or be synonymic with other names from 

 different horizons, future investigations will disclose. 



Cliothyris crassicardinalis White. 

 PL LXXI, fig. 8«. 

 Athyris crassicardinalis White, 1860: Jour. Boston Soc. Nat. Hist., Vol. VII, p. 229. 



This species is referred to the genus Cliothyris on the strength of a 

 clause in the original description, which states that "occasional specimens 

 show fringes of considerable length" proceeding from the squamose growth- 

 lines. This, in conjunction with the shape, which is not markedl}- wider 

 than it is long, seems to make this reference secure. On the other hand, not 

 having had access to specimens from the type locality, and as the species 

 has never been figured, I can consider my identification as only provisional. 



In the Yellowstone National Park the type here called CI. crassicardi- 

 nalis ranges from the bottom to the top of the Madison limestone. It is 

 seen to be a rather small, nearly circular shell, slightly wider than long, 

 lenticular. Fold and sinus indicated only by a slight emargination of the 

 anterior outline. Beaks small and pointed, that of the ventral valve being 

 usually incurved so as to conceal the foramen. The surface is covered with 

 numerous imbricating lamellose expansions, which under good jjreservation 

 are seen to be subdivided into long spines. The large specimen figured on 

 PL LXXI, fig. 8a, measures 15 mm. in width by 14 mm. in length, but 

 the average size seems to be somewhat less than this. 



This form is perhaps identical with the one figured in Mon. U. S. Geol. 

 Surv., Vol. VIII, PI. XVIII, fig. 5, under the name of Athyris hirsuta. 



It is often extremely difficult in practice to separate CI. crassicardinalis 

 from other forms found in the same beds — that is, when one or both are 

 ill preserved in one way or another. Exfoliated specimens might easily be 

 referred to the allied genera Athyris or Seminula. On the other hand, 

 where single valves occur embedded in limestone, from which they break 

 exfoliated and with the convex side upward, concealing the area, it is very 



