PLATE 33. 
ig. 4: 173. 6. ATRYPA EXTANS. (Pag. 137.) 
| a. Dorsal valve. 1 6. Ventral valve. 
Fig. 2. 174. 7. ATRYPA NUCLEUS. (Pag. 138.) 
2a, Ventral valve. 2b. Dorsal valve. 2c. Profile view. 
Fig. 3. 176. 9. ATRYPA BISULCATA. (Pag. 139.) 
3 a. Dorsal valve. 30. Ventral valve. 3c. Cardinal view. 3d. Enlarged profile view. 3 e. Front view. 
Fig. 4. 177. 10. ArRypa DEFLECTA. : (Pag. 140.) 
4 a. View of dorsal valve. 4 6. Front view, showing the form of the two valves. 
Fig. 5. 178. 11. ArRYPA RECURVIROSTRA. (Pag. 140.) 
5 a. Dorsal valve. 50. Profile view. 5c. Cardinal view. 5d. Ventral valve separated from the dorsal. 
Fig. 6. 179. 12. ArRyPa Exieua. (Pag. 141.) 
6 a. Ventral valve. 60. Dorsal valve. 6c. Cardinal view. 6 d. Dorsal valve of a small and large individual. 
Pais. 7. 181. 14. Arrypa circuLvs. (Pag. 142.) 
7 a. Dorsal valve. ©7 6. Cardinal view. 7c. Profile view. 
Pio. 8.0. 182. 15. ArTRYPA AMBIGUA. (Pag. 143.) 
Sa&b. Usual form of the shell. 8 e. Front view in outline, showing two incipient plications in the sinus. 
9. Four valves represented precisely as they occur on the surface of a slab of limestone. 
Fig. 10. 183. 16. ArTRyYPA HEMIPLICATA. (Pag. 144.) 
10 a. Dorsal valve of a specimen of the ordinary size 10 b. Profile view. 10 ec. Front view. 
10 d. Dorsal valve and front view of a young specimen. 
10 €. Ventral valve of a large specimen, 10 f. Front view of the same. 
Bie. 1A, 184. 17. Arrypa (perhaps the young of A. extans). (Pag. 145.) 
11 a, b. Ventral and dorsal valves. llc. Front view, the dorsal valve below. 11 d. Profile view. 
Fig. 12. 185. 18. ArRypaA sSUBTRIGONALIS. ( Pag. 145.) 
12 a. Ventral valve. 12 b. Profile view, 12 c. Front, with the dorsal valve below. 
Fig. 13. 186. 19. Arrypa INCREBESCENS. (Pag. 146.) 
13 a, 6. Ventral valve and front view. 13 7, m,n, 0. Ventral valves and front views of two 
13 ¢, d. Ventral valve and profile view. larger individuals. 
13.e, f. Ventral valve and profile view of a more 13 p, r, s. Ventral valve, profile and front view of a 
gibbous form. larger specimen. 
13 g,h, 7. Front, profile, and ventral valve of a larger 13 ¢t, uw. Profile and front view of a gibbous specimen. 
and more rotund specimen. 13 w. Profile view of a very gibbous specimen. 
13 k. A small specimen of the western type. 13 a, y. Front and cardinal view of the same. 
Fig. 14. 187. 20. ArRyPa DENTATA. (Pag. 148.) 
14 a. Dorsal valve. 14 6. Front view of the same, the dorsal valve below. 14 c. Profile view. 
Fig. 15. 180. 13. Arrypa MoDEsTA. (Pag. 141.) 
The two upper figures are of the dorsal and ventral valve of a specimen above the common size; the lower 
figure is of a small specimen, having the same characters. 
Fig. 16. 188. 21. AvRypa sorRDIDA. (Pag. 148.) 
