PLATE 6. 



Page 

 Fig. 1. Orthis lepidus 46 



1 a. Vontrul view of a s|)Ocimen, natural size. 



1 b. Dorsal view, natural size. 



1 c, d. Ventral 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 6. 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 «. Profile of the above. 



if. Cardinal view of the same. 



2 g, A. 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 Ac The interior of a dorsal valve, showing a thickening of the cardinal process. 

 2 /. An enlargement of the surface, showing the character of the stria, the ordinary puncta, and 



the elongate tubular openings. 



2 m. A cast of the dorsal valve of the same species, from Cumberland, Md. 



Fig. 3. Okthis VANnxEMi 47 



8 a, b, Ventral and dorsal views of a young individual. 



8 c. Ventral view of a specimen of medium size, presenting the ordinary form of the species. 



3 d. A ventral view of another individual. 

 8 e. Profile of a specimen. 



Zf. A. ventral view. 



i g. Dorsal view. 



S h. Ventral view of a large individual — the largest which can be satisfactorily referred to this 



species. 

 3 i. Dorsal view of the above. 

 3 At Profile of the same. 

 3 I. Cardinal view of the same. 

 S m. The interior of a ventral valve. 

 3 n, 0- The interiors of dorsal valves. 

 3 p. An enlargement of the surface striae, showing the puncta and tubular openings enlarged to the 



same degree as fig. 2 /, ofiering a comparison of the character of striae mode of bifurcations, 



tubular openings, etc. 

 8 r. A cast of a ventral valve supposed to be of this species, from -Cumberland, Md. 



