PLATE 52. 



P»ge 



Fig. 1-7. AvicuLA COMMUNIS. 286 



1. A cast of tlie left valve which has been transversely compressed, elevating the anterior and 



depressing the posterior wing. The radii are pretty regularly interrupted by the concen- 

 tric stria;. 



2. A smaller individual in which the shell is well preserved, showing the stronger and in- 



termediate finer radii. 



3. The interior of the left valve of a specimen of this species, in which the anterior wing is 



imperfect, as well as the cardinal margin of the posterior wing. 



4. The cast of the interior of a smaller specimen, having the posterior side and extremity of 



the wing broken off. 

 6. The right valve, from which the shell has been partially removed. The radii are much 

 more nearly equal, than on the opposite valve. 



6. The interior of a smaller specimen, in which the radii are more equal. 



7. A smaller individual (apparently of the same species), having the posterior side and base 



broken off, and the anterior side entire. 



Fig. 8. AviCULA PAUCIRADIATA. 287 



8. The interior of the specimen described. 



Fig. 9, and 10? Avicula textilis. 288 



9. The left valve of this species, preserving the posterior wing and the greater part of the 



body of the shell, the anterior portion being broken off. 

 10? The interior of a left valve, which, in the general form and obliquity of the body of the 

 shell, corresponds to this species, but the wing is shorter. The abrupt separation between 

 the body of the shell and the wing may be due to pressure, which has produced a slight 

 folding along that line. 



