472 GEOLOGICAL SURVEY OF THE TERRITORIES. 



2. Ostrea Small specimens, of perhaps two or 



three species. 



3. Qryplicea A small species of form of the G. 



dilatata. 



4. Gamptonectes Specimen imperfect ; may be G. 



helUstriata, M. and H. 



5. Pecten Part of a valve of a rather large, 



strongly costate species. Not a 

 true typical Pecten. 



6. Pinna l:s"ear P. opalina, Quenstedt. 



7. Gervillia Mont^n^nsis, Meek.* 



8. Gervillia Somewhat larger than the last, but 



not costate. 



9. Mytilus ..." Has angular umbonal slopes, and 



only concentric markings. 



10. Modiola ( Vulsella) suhimhricata, 



Meek.t 



11. Modiola {Vulsella) A shorter, wider, and less arcuate 



species than the last. 



12. Trigonia J. wenmwa, Meek.t 



13. Trigonia Montanaensis, Meek,§ 



14. Grassatella ("?) It has the external appearance of 



this genus, but may belong to 

 some other. 



15. Grassatella (?) Internal casts apparently of species 



of this genus. 



16. Gucullcea Casts. 



17. Astarte (?) „ .... A small shell like some of the Juras- 



sic species sometimes referred to 

 this genus. 



18. Unicardium Casts apparently of a species of this 



genus. 



19. Myacites {Pleurornya) suhcom- 



^ressa, Meek.ll 



* A medium-sized, very oblique species, with posterior ear flattened and of moderate 

 size, angular at the extremity, and equaling, on the hinge line, about half the length 

 of the valves ; body portion of the valves rather slender, nearly straight, or a little 

 arched, ranging at an angle of 28° to 30° below the hinge line, in the left valve con- 

 vex, in the right flattened, or less convex than in the other. Surface of both valves 

 marked by fine concentric striaj, and a few stronger farrows of growth, crossed on the 

 body part of the left valve, by a few slender radiating cost;©, separated by wider 

 spaces. 



t This is very like Modiola imhricata, Sowerby, as illustrated by Morris and Lycett, in 

 their Mouogr. Moll. Gr. Oolite, PI. IV, Fig. 2, excepting that its anterior ventral por- 

 tion, in front of the umbonal ridges, is more prominent, and its posterior basal extrem- 

 ity more produced and narrowed. It is much less like Sowerby's original figure of 

 that species. 



t A tine species of the type of T. costata of the Old World, but differing from that and 

 the other allied forms, in having the radiating costie of the corselet, or posterior dorsal 

 region, all of uniform size. 



1^ Of the type of T. signafa, Agassiz, but differing in its proportionally shorter form, 

 ■with smaller nodiferous costse, while it has a row of nodes down the anterior lateral 

 region of each valve, nearly as in T. navis, Lamarck. 



II Resembles some varieties of Pleuromyafemiginea and P.impressa, Agassiz, but has the 

 anterior end shorter and more truncated, the concentric ridges of less regularity, and the 

 slight concavity extending fj-om the beaks to the anterior basal margins of the valves, 

 either entirely 'wonting or very feebly marked. I have fully described and illustrated 

 this shell in the unj)ublished paleontological part of Mr. King's report. 



