No. 186.] 



41 



EENSSELiERIA SUESSANA. 



Fig. 1. The dorsal valve, showing the thickened processes at the base of the crura, 

 the dental fossets, and the minute foramen at the beak. The descending pro- 

 cesses, and tlie abrupt bending of the crura which are joined in a plate below 

 with the slender central process, are all shown in the specimen from which this 

 figure is made. 



Fig. 2. A diagram presenting a profile view, showing the relations of the parts de- 

 scribed. 

 These figures are enlarged to about one and a half diameters. 



Renssel^ria ovoides. 



3 



Fig. 3. Interior of the ventral valve, showing the foramen, tlie large dental lamellse, 

 muscular impressions, etc. 



Fig. 4. The interior of the dorsal valve of the same species, showing the thickened 

 processes at the beak, the crura, the loop and the narrow longitudinal plate, 

 which together so much resemble a bird's tongue with the hyoid bones. 



Fig. 5. A diagram presenting a longitudinal section of the two valves, showing the 

 crura, the descending process, etc. The dark line in the dorsal valve, between 

 the base of the crura and the shell, indicates the foramen described as ex- 

 tending from the beak into the cavity of the shell beneath the bases of the 

 crura. In the ventral valve a low medio-longitudinal septum is shown; while 

 the darker and more elevated ridge is a continuation from the base of the 

 dental lamellae, which limits the muscular area. 



[Assembly No. 186.] 



