PLATE 16. 



Page. 



Fig 1. Pteria linguiformis 32 



1 , a. A right-side view of an internal cast, with the projecting extremity of t lit- posterior wing 



broken away. 

 1,6. A slill more imperfect cast of a left valve. 

 1, c. A light-side view of a very small, young specimen. 

 1, rf. A left-side view of a larger example. 



Fig. 2. Pteria Haydeni 33 



2,o. A left-side view, natural size, copied from the original figure of the type-specimen (prob- 

 ably a young shell |. 

 2,6. The same, somewhat magnified. 



Fig. 3. Pteria (Oxytoma) Nebrascana 34 



3, a. A left-side view of a medium-sized specimen. 

 3, b. The same, of a large, imperfect specimen. 



3, c. Surface-markings, magnified. 



Fig. 4. AnomiaI subtrigonalis 22 



4, a. Au external view of the type-specimen, consisting of a east of the upper valve. 



4, 6. A different view of parts of both valves, perhaps of the same shell. 



Fig. 5. Sy'NCYCLonema rigida 27 



5, a. A medium-sized left valve. 



5, b. An internal east of a somewhat larger right valve. 



Fig. 6. Chlamys Nebrascensis 25 



(i, a. A left ? valve of one of the largest type-specimens, with one of its auricles broken away. 

 0, 6. A side view of the same, showing its convexity. 



6, e. A smaller, proportionally narrower specimen of same, with auricles broken. 



Fig. 7. Gervillia sobtortuosa 65 



7,o. A dorsal view of tho broken and exfoliated type-specimen, with tin.- two valves united, 



and the wanting posterior portion restored in dim, Hat shade. 

 7,6. An internal and hinge view of right valve of same. 



7, c. The same view of the left valve. 



Fig. 8. Gryi-ii.ea vesicularis? 20 



8, o. Exterior of lower valvo. 

 S,b. Internal view of same. 



