'KI.I.IIlKAN' IMA I \ 



the aiitero-caidmal margin of tin- >hi-ll: po-tc-rior -car indistinct, larger tlian the 

 anterior, situated a short -li-tancr beneath the post-cardinal margin. I'allial line 

 faint, -imple. -nlniiaiyinal. 



It is p<> il>le that this specie- is not distinct from the ' 'tirt,tnt.i <;l!ttiiii of 

 Hilling. Mix ti^'iire- of that -pe.-ies looks so much like the shell above described 

 that I am nearly -ati>tie-d that they must be congeneric at least. It might l>e a 

 U'hiffll'i. tint it i- not a true < om pared with / <>i<it.i it appeara 



that iu the Canadian -hell the beak- ,m> situated farther back from the anterior 

 extremity, the uinhonal ridge is rounded instead of angular and the outline different, 

 especially that of the posterior end. which i- also wider. 



/ locality J tli.- niKldl.- third f tin- Tr.-nton shul. - ^x. tnlli* .-nutli 



of Cann-.n Falls. Mnin.-MHa uuetonei -.f 



York. In '' unt\. Ivntu-'kv. 



I'r.h'lll... \i;l>i\ SDBBBBOTA I'lrirli. 

 1-I.ATE X! a-17. 



1'lethowrdia tulx,. n. 1^2 MtioUwnlh Ann. Krp. Oeol. and I Sur. Mftin., p. 846. 



1 small. Imt little oblique, exceedingly ventricose, short, sul>elliptical in a 

 si.lo view, with the dorso-ventral diameter much the longest. Beaks very prominent, 

 large, strongly incurved, nearly terminal; nmbonal ridge strong, sharply rounded, 

 with the cardinal and posterior slopes very abrupt and nearly flat. Anterior end 

 very short, the part in front of the beaks of casts consisting chiefly of the sharply 

 defined lobe-like filling of the anterior muscular impressions. Anterior and poste- 

 rior margins gently convex, subparallel; ventral edge sharply rounded. Hinge line 

 -hort, scarcely extending posterior to the urabonal ridge, as seen in a side view. In 

 the casts there is a depression beneath each beak that is prolonged on each side 

 around the mu.-cnlar -car. The escutcheon seems to have been narrow, but the 

 internal ligament supports at the posterior end of the hinge line have left two 

 strong grooves, one on each side. 



This species, though clearly congeneric with /'. umbonaia, is so readily di-tin- 

 that comparisons are unnecessary. 



formation an./ Ineality. -Galena shales near Cannon Palls, Minnesota. 



-37 



