186 LECTURES ON MOLLUSCA. 



with stout knobs or keels, and are very beautiful objects under the 

 microscope. The teeth of Cerithiopsis are said to resemble Triton; 

 but the tentacles are more like those of Tornatella. The siphon-pipe is 

 extremely short, not protruding beyond the notch of the shell. In 

 Triforis, the whirls turn the wrong way, and the lip of the shell is 

 often twisted into pipes for the reception of the breathing and excur- 

 rent ducts. The third pipe behind, which gave the name to the genus, 

 is simply the relic of a former mouth. The shells in each group are 

 sometimes so like each other that they can scarcely be distinguished, 

 except by the direction of the whirls. Yet the animal of Triforis is 

 said to belong to the true Cerites. 



'S 



? ? Family Cancellariad^e. 



The true position of this family is not yet ascertained. The Cancel- 

 larias are singularly beautiful shells, always elegantly sculptured, 

 with a few small plaits on the pillar, which are sometimes obsolete. 

 Often the pillar is hollow ; and instead of a notch or short canal for 

 the breathing tube, there is only an angular pinch in the shell. The 

 siphon pipe is extremely short; but as to the important characters of 

 the head, the learned differ. Messrs. Adams say that it has neither 

 tongue, teeth, nor proboscis ; and Deshayes states that it is a vegetable 

 feeder. Dr. Gray, however, places it near the Muricids. The genus 

 is confined to tropical seas and rather deep water ; but an allied form, 

 Achnete, lives in Greenland, and visits the New England shores. In 

 the boreal group Trichotropis, so called from the beautiful hairy fringes 

 on the epidermis ; there are no plaits on the pillar. The animal has 

 been described by some authors as having a retractile proboscis ; by 

 others as having a muzzle. Whether widely different animals have 

 been grouped together, or whether great mistakes have been made, 

 remains to be seen. 



In the foregoing families, when the shell has been partially covered, 

 it has been not by the mantle (as often stated) but by the broad and 

 fleshy foot. In the aberrant family of Fig-shells, however, the foot, 

 though widely extended, is very thin ; and the shell is partly enveloped 

 by two flaps of the mantle, as in the Cowries. 



Family FicuLiDiE. {Fig- Shells.) 



The shells of this group are singularly elegant; very thin, pear- 

 shaped, finely cancellated outside, with a long wide canal, which 

 protects the still longer breathing pipe. The animals are beautifully 

 painted, with markings of various colors. They stretch out their long 

 white necks, with flat heads, and large black eyes, and crawl very 

 rapidly over the sands. There are very few species ; one inhabiting the 

 Pacific shores of tropical America, another the Atlantic, and the rest 

 the East Indian seas. 



We now come to animals having a very different appearance, and 

 furnished with shells having no similarity in shape with those hitherto 

 described. The shells were associated by the conchologists with the 



