452 



J. F. ILLINGWORTH, 



secting needle. The little stream of water carries away each bit as 

 it is dissected ofif, and if the force is not too strong the nerve fibers 

 are not disturbed. The force of the jet is easily controlled by regu- 

 lating the hydrant. 



External features. The shell (Fig. A) is irregularly oval 

 in general outline, presenting the appearance of a symmetrical, flat- 

 tened dome, with the apical fissure nearer the anterior end. This 

 fissure is oval, conforming in shape to the outline of the shell. The 

 edge of the shell is finely crenated, and small furrows run from fine 

 marginal notches to the apical opening. The successive lines of growth 



Fig. A. 



Fig. A. Shell of Lucapina crenu- 

 lata. 



Fig. B. Dorsal view of the animal. 

 Drawn from a slightly contracted spe- 

 cimen. 



Fig. C. Ventral side of the same 

 specimen. 



Fig. B. 



Fig. C. 



are usually well marked running parallel to the border. The inside 

 is very smooth and pearly white. Near the apical opening, there is 

 a thickened part, irregular in outline surrounding the fissure, which 

 uneven surface serves as an attachment for the muscles of the mantle 

 fissure. The shell during life remains almost hidden in the mantle 

 covering. When the animal is disturbed, however, the mantle is con- 



