Mr. W, H. Benson on Camptonyx. 339 



shelly tube which communicates with the interior in so many of 

 the mountain-loving oriental Cyclostomidse. 



In Mr. Woodward^s drawings, the position of the ocular 

 points, widely separate from each other, is on the upper side of 

 the head. The}^ are sessile at the middle of the hinder part of 

 the base of the short obtuse tentacula, and are visible only from 

 above; whereas in Gray's figure of Ancylus (no. 52. p. 2i6, ed. 

 noviss. Turton) the eyes appear below, and are stated to be placed 

 on a small lateral lobe on the side of the base of the triangular 

 truncated tentacle*. In LymncBa, where the eyes appear on the 

 upper side of the head, they are in front, prominent, and ap- 

 proximate to each other. The position of the eyes in Pythia 

 (Scarabus), which I had an opportunity of examining some 

 twenty-three years ago at Calcutta, more nearly represents that 

 of the corresponding organs in Camptonyoo. 



The littoral genus Siphonaria, which Dr. Gray places between 

 the Auriculidse and Cyclostomidse, is remarkable for the presence 

 of a deep siphonal groove on the right side. Again, the large 

 Tertiary fossil genus Valenciennia, Rousseau, supposed to have 

 been an inhabitant of brackish water, has a channel running 

 from the under side of the beak of the shell to the right side of 

 the aperture, much like the dorsal one of Camptonyx. It is 

 supposed by M. Bourguignat to serve as a sheath to a siphonal 

 tube. It probably communicates, as in Camptonyx, with the 

 respiratory orifice, and does not necessarily contain a special 

 organ. The strong concentric ribs of Valenciennia present a 

 curious analogy to the rugose surface of Camptonyx, 



17th April, 1858. 



EXPLANATION OF PLATE XII. 



Fig. 1. a, Shell of young Camptonyx viewed from the aperture; b, dorsal 



view; c, side view. 



Fig, 2. d. Adult shell ; aperture ; e, dorsal view. 



Fig. 3. Live animal in the shell; /, siphon. 



Fig. 4. Dead animal in the shell; g, muzzle. 



Fig. 5. Dead animal extracted from the shell, dorsal view. 



Fig. 6. Ditto; h, respiratory orifice; i, adductor muscle. 



Fig. 7. Teeth. 



All the figures are greatly magnified. 



* Dupuy's description of the animal of Ancylus, and the details given 

 in Moquin-Tandon's ' MoUusques de France,' plates 35 & 36, help to con- 

 firm the dififerences observed. 



22* 



