Hogg, on the Lingual Membrane of Mollusca. 101 



gain access to the interior. In some respects the odontofore 

 of the whelk resembles that of vegetable feeders. 



Chitonidie, with their liorny jaws and long, slender 

 tongues bristling with numerous rows of teeth, tipped with 

 strong, dark- coloured claws, two of which are more pro- 

 minent than the rest, whose general structural characters 

 closely resemble Patellidae, find a place among a very different 

 class. Strom nearly a century ago observed both a general 

 and anatomical resemblance between the Coat-of-mail (Chiton) 

 and Limpet (Patella), and noted the fact that, although both 

 were vegetable feeders, and the structure of their shells differ, 

 there is sufficient general resemblance to induce systemato- 

 logists to place them in one family. Fissurella is evidently 

 a near relation of Patella ; it is furnished with nearly the 

 same kind of mandibles as well as odontofore. Cuvier be- 

 lieved Fissurella and Haliotis to be closely allied. Indubitably 

 the latter bears in many of its external characters a striking 

 resemblance to Patella ; but if a comparison of its lingual 

 membrane be made, we at once discover much diversity 

 both in form and arrangement. Dr. Gray sejjaratcs Fissu- 

 rellidae from Patellidse by arranging Dentalium between 

 them ; and although Crepidulidse differ very slightly from 

 Patellidse, he nevertheless places them widely apart. 



Trochidse, while they resemble in many respects the 

 families just spoken of, the odontofore differs in not unim- 

 portant particulars. The median portion of the band is 

 armed with many teeth, and the plurse with numerous regu- 

 larly arranged uncini, grow gradually more and more simple 

 and slender as they recede from the central row. In Trochus 

 cinerarius (PI. XI) the medians are large and heart-shaped, 

 with five somewhat similar teeth on either side, and pleurae 

 armed with ninety uncini. (Formula cc 5 — 1 — 5 — x.) 



Litorinidae, which are found freely scattered over every 

 quarter of the globe, scarcely differ in any particular, and 

 are almost exclusively vegetable feeders. A few of this 

 family seem to prefer sponges and zoophytes, but this prefer- 

 ence is shown only when such structures are loaded with 

 young diatoms or vegetable spores ; these they scrape off, 

 and the animal body is left untouched. The lingual mem- 

 branes of all are alike, save in the most unimportant par- 

 ticulars. Osier, in the * Phil. Trans.,' 1832, tolerably accu- 

 rately describes this phytivorous family, which, he says, 

 " have three distinct modes of feeding. They browse with 

 opposite horizontal jaws, they rasp their food with an armed 

 tongue stretched over an elastic and movable support, or 

 they gorge it entire. Ti'ochus crassus (fig. 48) is an example 



