62 HETEROPHROSYNID^E. 



similis; but it is not so turreted, and the spire has a 

 blunt instead of a sharp point. A dead specimen from 

 Falmouth is marked with nexuous and close- set longi- 

 tudinal striae, arising probably from a partial decay of 

 the surface. 



A comparison of the description of this species with 

 that of J. diaphana, as regards their soft parts, may 

 serve to show that the tentacles of all the Mollusca, 

 whether univalve or bivalve, are nothing more than a 

 development of the mantle, endued with special sensi- 

 bility as organs of touch or of some other less direct 

 medium of sensation. In some cases (e. g. Chiton, Ho- 

 malogyra, certain species of the Bulla family, and infe- 

 rior kinds of the naked Mollusca) tentacles are entirely 

 wanting ; while in others (e. g. the present species of 

 Jeffreysia, and most of the Pulmonobranchiata) the 

 usual pair becomes double, as if for the purpose of in- 

 creasing the sense of perception. In Pecten and those 

 bivalves which have the mantle open the tentacles are 

 numerous ; the cirri fringing the tubes of the majority 

 of bivalves which have the mantle more or less closed 

 appear to be supplementary organs of a similar nature ; 

 and so are the appendages of the head and opercular 

 lobe in Trochus, Rissoa, and many univalves, as well as 

 the cilia that cover the body in Stilifer. But I must 

 not get out of my depth. We cannot all be physio- 

 logists, 



" And take upon us the mystery of things, 

 As if we were God's spies." 



3. J. globula'ris*, Jeffreys. 



J. globularis (Jeffreys, MS.), F. & H. ir. app. p. 268, pi. crxxiii. f. 5. 



Body dark-grey, finely streaked with purplish-brown, paler 

 underneath : snout forming two short cylindrical processes, 



* Globular. 



