PLATE 108. 



Page 



Fig. \ a -f. Renssel^sria cumbbrlandi^. 464 



\ a,b, c. Ventral, dorsal and profile views of an entire specimen. 



1 d, e,f. Ventral, dorsal and profile views of an imperfect specimen, the dorsal view showing 

 the triangular foramen which results from the removal of the deltidial plates. 



Fig. 2 a, b, c. Rens8EL.(ERIA intermedia. 463 



2 a. Dorsal view of a well-preserved specimen. 

 2 b, c. Profile views of different individuals of the same species. 



Fig. 3 a - »«. Renssel.«;ria marylandioa. 461 



3 o. Dorsal view of a specimen of this species. 



8 b. Ventral view of the same. 



8 c. Profile or lateral view of the same. 



3 d. Cardinal view of the same, having the ventral side upwards. 



8 «. Front view ( not well shown in the figure). 



8/. The apex of the ventral valve (somewhat enlarged ), showing the foramen, and the delti- 

 dial pieces forming the lower side of the foramen. The outer margins are too thick in 

 the figure. 



8 g. The interior of the ventral valve, showing the teeth, the dental plates, and muscular 

 impression. 



8 A. A similar specimen where the cavity of the valve is not so deep, showing the form of 

 the muscular area and the places of the adductor muscles. The iimer edges of the dental 

 plates are seen extending into the cavity of the foramen. 



8 t. The rostral portion of the two valves joined at the hinge : the dorsal valve is down- 

 wards, showing the bases of the crural plates and the ridges proceeding from these. The 

 opening of the foramen between the bases of the crural processes is very perceptible. 



8 fc. The interior of the upper part of a dorsal valve, showing the broad hinge -plates, the 

 bases of the crura, the elevated median process, and the foramen below the apex. 



3 /. Diagram of the interior of the dorsal valve, showing hinge-plates, dental sockets, apicial 

 foramen, crural processes and crural plate. In the specimen from which this figure is 

 taken, these processes are all encased in crystalline matter, the form and direction of the 

 parts alone being visible. The slender process at the base of the crural plate is broken 

 off"; and since its entire length is unknown, the base alone is represented. 



3 7n. A diagram representing a longitudinal section of the shell, and the internal apparatus 

 of the .two valves when connected. 



