PLATE 6. 
Page 
Fig. 1. Orthis lepidus. 46 
1 a. Yentral view of a specimen, natural size. 
1 b. Dorsal view, natural size. 
1 c. d. Yentral and dorsal views, enlarged to two and a half diameters. 
1 e,f. Profile, and front views, same enlargement. 
Fig. 2. Orthis penelope..... . 50 
2 a. Dorsal view of a young individual. 
2 b. A ventral view of an older individual. 
2 c. A dorsal view of a specimen of the ordinary size. 
2 d. Dorsal view of a large individual. 
2 e. Profile of the above. 
2/. Cardinal view of the same. 
2 g, h. The interiors of ventral valves, showing the form of the muscular impression. 
2 i. The same, with the shell much thickened around the muscular impression and towards the 
front. 
2 k The interior of a dorsal valve, showing a thickening of the cardinal process. 
2 l. An enlargement of the surface, showing the character of the striae, the ordinary puncta, and 
the elongate tubular openings. 
2 wi. A cast of the dorsal valve of the same species, from Cumberland, Md. 
Fig. 3. Orthis vanuxemi. 47 
3 a, b, Ventral and dorsal views of a young individual. 
3 c. Ventral view of a specimen of medium size, presenting the ordinary form of the species. 
3 d. A ventral view of another individual. 
3 e. Profile of a specimen. 
3 /. A ventral view. 
3 g. Dorsal view. 
3 h. Yentral view of a large individual—the largest which can be satisfactorily referred to this 
species. 
3 i. Dorsal view of the above. 
3 k. Profile of the same. 
3 l. Cardinal view of the same. 
3 m. The interior of a ventral valve. 
3 n, o. The interiors of dorsal valves. 
3 p. A n enlargement of the surface striae, showing the puncta and tubular openings enlarged to the 
same degree as fig. 2 l, offering a comparison of the character of striae mode of bifurcations, 
tubular openings, etc. 
3 A cast of a yentral yalye supposed to be of this species, from Cumberland, Md. 
