TONGUES OF MOLLUSCA. 73 



The first are distinguished by having an immense number 

 of very minute teeth, arranged in long transverse rows, 

 and all similar in shape, except the central ones. These 

 belong to animals contained in the order Pulmonifera of 

 Milne-Edwards, which corresponds with the Pulmonata of 

 Cuvier ; and the illustrations I have prepared are tongues 

 of Limnceus stagnaliSj Helioc pomatia, a species of Bulimus 

 from California, and Siphonaria gig as, a very interesting 

 sea-MoUusk, with a shell like a limpet. 



The three other groups, which are quite as distinct from 

 one another as they are from that just mentioned, belong to 

 animals all of which are thrown together into the one order 

 Prosobranchiata by Milne-Edwards; but inCuvier^s arrange- 

 ment we find a separate order corresponding with each. 



The first of these I shall mention is his order Cyclo- 

 branchiata, including the Limpets and several allied ge- 

 nera, which all possess a peculiar type of tongue, distin- 

 guished by its great length and by several well-marked 

 characters in its teeth. In the first place, there is no tooth 

 in the middle line, but they are arranged symmetrically on 

 each side of it, in alternate central and lateral sets, so 

 that, strictly speaking, two rows go to form one complete 

 series (PI. IV.) ; then the teeth themselves are remarkable 

 for their dark-brown colour, their strength, and the bold 

 manner in which they project from the membrane, remind- 

 ing one of the strong prickles on a rose-bush. The speci- 

 mens illustrating this type of teeth are. Patella vulgata, 

 one of the preparations showing the entire length of the 

 ribbon, and accompanied by the shell of the animal from 

 which it was taken; Patella pellucida, which, compared 

 with Patella vulgata, afibrds a good example of strongly 

 marked specific difPerences ; and several American species, 

 including Patella, Scurria, and Acmcea. The Chitons, which 

 were placed in this order by Cuvier, have been properly 

 separated by later naturalists. 



