138 bloomer: malformed specimens of anodonta cygnea, l. 



Specimen B was collected in March and exhibits only a slight 

 indentation across nearly the whole of both valves. Both of the gills 

 on the right side are deformed, and the outer gill of the left side 

 (fig. 2). The mantle-lobes are complete, but the left one shows a 

 thickened growth on the inner side. Commencing near the median 

 line and close to the base of the gills, it continues in a slightly 

 postero-ventral direction towards the edge ; as it proceeds it narrows 

 and increases in thickness until near its termination, where it becomes 

 circular, is deeply pigmented, and has a well developed tentacular 

 fringe, differing only in size from that bordering the inhalent aperture 

 of the branchial chamber (fig. 2. a. d.). 



Specimen C (PI. vii, figs. Bi, B2) was collected about three years 

 ago. Though not exhibiting any signs of fracture it is a very deformed 

 shell, and when viewed from the end the valves are seen to be greatly 

 contorted. The left valve is deeply indentated, but the lines of 

 growth are normal. The right valve shows a transverse malformation 

 and externally has two parts with semicircular lines of growtli, which 

 later have assumed a normal course, while on the inside there are two 

 inverted cup-like growths. 



The contorted form of the shell has given rise to great deformity 

 in the animal; thus the larger portion of the viscera was in the anterior 

 portion of the left valve, which gave rise to a displacement of the 

 pericardium, heart, and rectum. The outer gills of both sides were 

 deformed, and the foot was enlarged and forced into a more anterior 

 position than is usual. The left mantle-lobe was penetrated by the 

 shell. 



The results of the examination of these three interesting specimens 

 tend to point to the following facts : 



a. that the animal is able to repair even extensive damage to the 

 mantle-lobes, but is not able to make good injuries to the 

 gills. 



h. the gills are the first organs to be affected. 



c. the animal is capable of living and thriving with very much 

 aborted respiratory organs, and with considerable displace- 

 ment of the various internal organs. 



EXPLANATION OF PLATE VIL 



Anodonta cygnea, L. 



Fig. Ai. Left valve of shell of specimen A. 



Fig. A2. Inner side of same. 



Fig. Bi. Right valve of specimen C. 



Fig. B2. Left valve of same. 



All the figures are reduced one third. 



