96 



NOTES ON SOME FURTHER MALFORMED 

 SPECIMENS OF ANODONTA CYGNEA, L. 



By H. H. bloomer. 



(Plate vii). 



Since my last notes on this subject appeared in the Journal,' 1 have 

 received from Mr. S. P. Bolton several more injured specimens, among 

 which were two showing other interesting points of malformation. 

 One bore indications of an injury to the left valve — the fracture 

 extending in an anterio-ventral direction from the umbo to the edge of 

 the shell, which had been repaired, the inner layer now being continuous 

 with that of the other portion of the valve. There is also an indent- 

 ation on the right valve opposite to the injury on the left one. The 

 free edge of the left mantle lobe appears irregular in its growth, and 

 the portion of the lobe covering the injured part of the valve is much 

 thicker than the other portion. The left labial palps are somewhat 

 aborted, and have a more ventral position than the right ones. The 

 outer one for a little distance is fused with the mantle lobe. 



In the other specimen the right valve was apparently stove in a 

 little anterior to the centre of it, and just below the umbo. The injury 

 at the time of occurence must have been considerable, and penetrated 

 into the body of the animal itself. The injured valve was repaired 

 and the subsequent growth of the shell was nearly normal. The left 

 valve is intact. The gills suffered the greatest injury, while strange to 

 say the mantle lobes appear to be normal. The left gills are severed 

 from their distal edges to close to the outer supra branchial chamber 

 (PL vii, fig. i). 



The right inner gill is not injured so much and the laceration does 

 not extend so far dorsally, while, however, the free portion of the 

 right outer gill is for some distance anterior to the injury, entirely 

 missing (PI. vii, fig. 2, r.o.g.), and the portions near the base on both 

 sides of the gap have fused with the mantle lobe. 



A transverse section across the injured portion of the animal, 

 shows both the left supra branchial vessels to be somewhat distorted 

 and bent inwards, and the right inner gill exhibits the subsequent 

 fusion of its injured portions. 



(i) Journ. of Malac, 1900, vol. vii, p. 177. 



