178 



BLOOMER : ON ANODONTA CYGNEA. 



side of the left outer gill, very little remaining of the left inner gill. 

 The left outer supra-branchial canal (fig. i. sc) is considerably larger 

 than the right outer one. 



In the second specimen there is a large fracture of the right valve, 

 which at the time it occurred evidently forced in a large mass of 

 the valve. The animal afterwards rebuilt the shell beneath the 

 fracture, the new portion consisting of the calcareous and nacreous 

 layers only. On the inner side of the right valve there has arisen a 

 thin ridge of shell 13 mm. long, and 7 mm. high, which passes in a 

 posterior direction and is set at right angles to the valve. Dorsally 

 there is a second, much smaller ridge, running parallel with the former 

 one. The animal exhibits very few signs of injury. The ridges, 

 mentioned above, have penetrated the posterior adductor muscle, the 

 right portion of which has spread out and become forced into a more 

 anterior position than the left portion, thus deforming the right kidney. 

 Other than this the animal appears quite normal. 



Fig. I. — Transverse section oi Anodonia cygnea, L. 



F. foot, I. intestine, K. kidney, L.l.G. left inner gill L.O.G. left outer gill 

 M. mantle, P. pericardia] cavity, R. rectum, S.C. left outer supra-branchial canal, T. 

 typhlosole, V.C. vena cava. 



