6.2 HETEROPHROSYXID.E. 



si mills; but it is not so tiuTeted, and the spii'e lias a 

 blunt instead of a sharp point. A dead specimen from 

 Falmouth is marked with flexuous and close-set longi- 

 tudinal striiC;, arising probably from a partial decay of 

 the sm'face. 



A comparison of the description of this species ^s-iih 

 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 dii'cct 

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

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

 rior kinds of the naked ^lollusca) 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. ghhularis (Jeffreys, MS.), F. & H. iv. app. p. 268, pi. cxxxiii. f. 5. 



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

 underneath: smut forming two short cylindrical processes, 



* Globular. 



