Mr. W. H. Benson on Tanysiphon. 407 



Otina was formerly confounded with Velutinaj a marine genus. 

 I showed that it was a lung- breathing animal, and arranged it 

 with Auriculidce, on account of the position of the eyes ; but the 

 form of the tentacles induced me, in my last work, to place it as 

 a tribe in the family Lymneadce. The discovery of Camptonyx, 

 however, with its similar terrestrial habitat, and having eyes in 

 the same position, indicates the necessity of forming a family 

 Otinida for the two genera. 



The form of the muscular scars in shells depends in great 

 measure on the form of the shell : thus, all very open-mouthed 

 shells, except HaliotiSy have a large horse-shoe-shaped muscular 

 scar, as that form of adductor muscle is required to keep the 

 shell on the back of the animal ; so that the form of the mus- 

 cular scar and of the shell depend on each other. 

 May 1, 1858. 



XXXVIII. — Characters o/ Tanysiphon, a new genus of Fluviatile 

 Shells, allied to the Myacidse. By W. H, Benson, Esq. 



[With a Plate.] 



In January 1846, when making one of my latest conchological 

 explorations in the vicinity of Calcutta, I procured on the muddy 

 shore of Tolly^s Nullah, near the bridge leading to Allipore, a 

 single valve of a Potamomya, and of another bivalve, apparently 

 allied to my ancient acquaintance Novaculina, which also inha- 

 bits the same water, but differing from it so much in the struc- 

 ture of the hinge, and the greater comparative length of the 

 siphonal scar, that I felt assured of its being the type of a distinct 

 genus, to which I assigned, in MS., the name Tanysiphonia, 

 Ten years later. Dr. Theodore Cantor having been appointed to 

 a medical charge on the banks of the small tidal stream in ques- 

 tion, I entreated his attention to a search for living specimens, 

 which I felt assured would be found at some depth in the mud 

 at low-water. He kindly answered my call, and after much 

 search by his people, transmitted to me a packet which con- 

 tained a few specimens of the desiderated shell among a greater 

 number of Novaculina, When shown by me to a well-known 

 conchological author, he doubted whether I had sufficient grounds 

 for separating the form from Novaculina. Dr. Cantoris atten- 

 tion being then called to the acquisition of the smaller form in 

 a living state, his kind exertions were rewarded by the capture 

 of live specimens in the following spring. These were trans- 

 mitted, in spirits, with a drawing, and some observations on the 

 external characters of the animal and its affinity, which I find 

 fully borne out by the specimens received. 



