REPORT ON THE MOLLUSCA. 7 



is differentiated and forms a distinct mass (labial projection, Bouviev), from which 

 spring the nerves supplying the probably gustatory parts (PI. I. fig 5, e). 



In TrocJms infundihulum each of these la1)ial projections gives off, distally, two 

 nerves, of which the greater {i) is the special nerve of the lips of the mouth, while 

 nearer the cerebral ganglion properly so called, there arises a large nerve {h) which 

 goes directly to the labial palp. 



The labial palps of Trochus infundihulum arc connected below the alimentary 

 canal, forming an infra-cesophageal commissure, as in Patella (this does not exist in the 

 Trochus figured by Haller ' ) and in all the Diotocardia, according to Bouvier.^ 



There can be no doubt as to the nature and use of these appendages (lalnal palps); 

 they are organs of sense, more tactile than the anterior tentacles. When greatly 

 developed [Ampidlaria, Trochus infundibidum, Glandina, etc.) they become important 

 exploring organs. In Bulimus (according to Ferussac) these palps exhibit on their 

 anterior surface a series of minute regular projections, the structure of which has not, 

 to my knowledge, yet been studied. 



Besides the forms hitherto enumerated, I have been able to study several other 

 species of Gastropods from great depths collected by the Challenger Expedition. 

 But, as was the case with the preceding species, I have only been able to examine 

 the anterior portions of the body, since the visceral mass had remained in the shells, 

 which were not to be destroyed. The most interesting point resulting from the 

 examination of these forms relates to the state of the organ of eight, 



Pleueotomatid^, 



5. Pleurotoma lepta, Watson. Station 157; 1950 fathoms. 



The head, the proboscis, and the tentacles are quite normal, except that the last 

 are entirely devoid of eyes : they exhibit neither a pigmented spot, nor even, like 

 Guivillea, a projection indicating a rudimentary eye. 



As in all the other animals of the group, the roof of the pallial cavity exhibits 

 a false gill (osphradium) (here very large) to the left of the functional gill. Watson 

 is mistaken in his description of its position/ 



G. Pleurotoma hrychia,y<l atsox).. Station 106 ; 1850 fathoms. 



This species is in the same condition as the preceding one as far as the tentacles 

 are concerned : no trace of an eye can be found on them. 



1 Untersuchungen iiber Marine RhipidogloBSen, i., Morpk. Jahrh., t. ix. (1884) pi. ii. fig. 3. 



' Systeme uerveux, morphologic generale et classification des Gasteropodes Prosobrancbes, Ann. Sci. Sal. (Zool.), 

 ser. 7, t. iii. p. 481. 



, ' Zool. Chall. Exp., part Ivii. p. 335. 



