PLATE 52 . 
Page 
Fig. 1-7. Avicula communis. 280 
1. A cast of the 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 strirn. 
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. 
o. 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. 
8. The interior of the specimen described. 
287 
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. 
