PLATE 90. 
Page 
Fig. 1-7. Orthis iiipparionyx. 407 
1. Cast of the dorsal valve of a younger specimen than that of the preceding plate. 
2. Cast of the ventral valve of a specimen of medium size, showing the lower part of the 
muscular impression hut faintly developed. 
3. A similar specimen, which preserves a portion of the shell. 
4. An older specimen, in which the cast of the muscular imprint is perfectly preserved. 
5 & 6. The interior and the cast of a very old shell. 
7. A portion of the surface striae enlarged. 
