PLATE IV I. 



Leg-end. pa. Posterior adductors. p. Parietal impression. 



aa. Anterior adductors. m Median impressions. 



da. Dorsal adjusters. b. Brachial muscular impression, 



va. Ventral adjusters. v. Vascular trunks. 



mm. Mesenteric muscular impression. v'. Vascular branches. 



CRANIP:LLA, CEhlert. 



i'age 1.53. 



Craniella Ulrichi, sp. nov. 



Fig. 1. A cast of the interior of a lower valve, somewhat restored on the i-ig-ht side ; showing- the strong 

 anteri. r and vei-y obscure i:)Osterior adductor impressions, and the marks of the vascular sin- 

 uses. The shell is convex and shows no evidence of attachment, though the external sui-face is 

 overgrown with abi-yozoan. Di-awn from a gutta-percha cast of a natural interior. X 1.5. 

 Trenton limestone. Minnea'polis, Minnesota. 



Fig. 2. The mternal cast of an upper valve, believed to be of the same species. The sigmoid vascular 

 impressions are simplei- than elsewhere observed ; the scars of the doi-sal adjustors and of 

 muscles accessoi-y to the anterior adductors (possibly the brachial muscles) are also apparent. 

 Drawn from a gutta-percha cast of a natural interioi-. X 1.5. 

 Ti-enton limestone. 3Iinneapolis, Mbmesoia. 



Craxiella Hamiltoni.e, Hall. 



Fig. 3. The interior of a lower \alve attached to a STKEPTiiL.\SMA ; showing the usual character of the 

 muscular scars, viz., anterior and posterior adductors, the ventral adjustors, and post-median 

 or mesenteric impression ; also the characteristic radiating vascular sinuses. 

 Hamilton group. Cananclaigua Lake, N. Y. 

 Fig. 4. The interior of an uppei- valve. 



Corniferous limestone. Falls of the Ohio. 

 The interior of an attached valve. Fi-om Pal.'eontology of New York, vol. iv, pi. iii, fig. 23. 

 Three individuals of diffei-ent sizes, attached to the surface of TropUMeptus cai-inatus. Opei-o 

 citato, pi. iii, fig. 19. 



Hamilton group. We.9ter?i New York. 

 The interior of a lower valve ; showing the usual mu.scular and vascuhir impressions, and very 



great thickening of the shell. X 2. 

 An uppei- vaive ; showing the modification of the surface from attachment to an individual of 



Spirifei' audaciilus. 

 Profile view of a normal shell, attached to Tropidoleptus carinatiis. 



Hamilton group. Canandaigua Lake, M. Y. 

 The exterior of an upper valve. From Thirteenth Rept. State Cab. Nat. Hist., p. 76, tig. 3. 1860. 



Hamilton group. We,itern Nexo York. • 



An upper valve, modified by attachment to the post-lateral portion of a right valve of Cypncardella 

 {Microdo?i) beUi.striata. 



Hamilton group. Canandaigua Lake, N. Y. 

 An individual greatly modified by attachment to Tropidoleptus carinatus. 



An internal cast of a large upper valve ; .showing the usual muscular scai-s and the peculiar 

 sigmoid vasculai- trunks with their i-amifications. 

 Hamilton group. Pratt's Falls, N. Y. 

 An internal cast of a very convex upper valve, greatly modified by attachment. X 2. 



Hamilton group. Canandaigua Lake, N. Y. 

 An intei-nal cast of an upper valve; showing the characteristic impressions. X 2. 



Hamilton group. Bellona, N. Y. 

 An internal cast of a convex and apparently free lower valve ; showing the closer approximation 

 of the anterior and postei-ior adductor scars than in the opposite valve, the deep inipresssion of 

 the mesenteric muscle, and the i-adiating- vascular sinuses. The figure is slightlv restored on 

 the left side. X 2. 



Hamilton group. Genterfield, N. Y. 



PHULIDOP8, Hall. 



I'ag-o Jo.i. 



Pholidops Tkentonensis, Hall. 

 Fig. 17. A slightly criished specimen. X 4. 



Trenton limestone. Middleinlle, N. Y. 



PhOLIDOI'S ClNCINNATENSIS, Hall. 

 Fig. 18. The exterior of a noi-mal specimen. X 4. 



Hudson River group. Cinammti, Ohio. 



Fig. 

 Fig. 



5. 



Fig. 



7. 



Fig. 



8. 



Fig. 



9. 



Fig. 



10. 



Fig. 



11. 



Fig. 

 Fig. 



12. 

 13. 



Fig. 



14. 



Fig. 



15. 



Fig. 



16. 



