360 MOLLUSCS. 



example of the Pellibranchs. It is slug-like in form, but without any tentacles. 

 The species figured (L. capitata) is a minute animal, about a sixth of an inch in length, 

 chiefly of a black colour, but occasionally somewhat transparent and colourless. 

 Alder writes that " this curious little animal is probably pretty generally diffused, 

 but on account of its minute size it may readily be overlooked. It is gregarious ; 

 and, wherever met with, it has usually been found in abundance, appearing when 

 contracted like little black dots scattered over the conferva on which it feeds." 



Limapontia capitata (much magnified). 



It lives between tide-marks, feeding upon small algaj, and deposits its ova in small 

 pear-shaped capsules, each containing about one hundred eggs. 



The only form belonging to this group, the position of which is 

 not settled, is the parasitic genus Entoconcha. The animal is worm- 

 like and spirally coiled, and attaches itself by the oral end (a) to one of the 

 blood- vessels (E), within the visceral cavity of a certain group of Echinoderms. 

 One species is found in Synapta, and a second (E. muelleri) occurs in the 

 trepang (Holothuria) of the China Sea. In the very early or larval state Ento- 

 concha is contained in a minute operculated glassy shell. The subsequent changes 

 between this and the perfect condition have not yet been observed. It is the 

 lowest type of Nudibranchiata, if indeed it really belongs to that suborder, which 

 is not absolutely certain, some authors even locating it near Natica. Were it not 

 for the form of the larva, one would hardly have supposed that this worm-like 

 creature belonged to the Mollusca at all. It has neither jaw nor radula, but the 

 mouth is adapted for sucking. The sexes, as in the typical Nudibranchs, are 

 united in the same individual. The female element (b) is somewhat anterior, the 

 male organ (c) being at the opposite extremity. The central portion of the animal 

 serves for a certain time as a nursing-pouch for the embryos, which subsequently 

 are extruded at an opening at the posterior end. Only one out of every hundred 

 or two hundred specimens of Synapta is infested with the Entoconcha. Pelsenecr 

 locates it next to Eulima among the Pectinibranchs. 



Covered-Gill Subgroup, — Suborder Tectibranchiata. 



This constitutes the second suborder of Opisthobranchiata, and includes 

 certain molluscs characterised by the possession of a lateral gill, protected by 

 the mantle, or a shell. The members of the group are hermaphrodite animals. 

 and differ from the Nudibranchs, not only in their respiratory organs, but 

 also in the possession of a true mantle, which, in the Nudibranchs, is repre- 

 sented by the dorsal shield. On the other hand, they show affinity with certain 



