58 LECTURES ON MOLLUSCA. 



and to the corresponding confusion of those who have to work-up their 

 achievements. The} 7 can even subsist in the severe winters of New 

 York, but shiver at the thoughts of Lower Canada and New England. 

 The Mediterranean appears to have limited their migration into Europe 

 to a very few aberrant species in the extreme south. In the East 

 Indies and Pacific islands, they again appear with something of the 

 prolific character which culminates in the United States. They are 

 known from the Paludinas by the edge of the mantle being fringed ; 

 they have no neck-lappets, but there is generally a rudimentary siphonal 

 fold. The muzzle is large and dilated ; the tongue long and slender : 

 the gills in a series of stiff, cylindrical plates. The operculum is 

 almost always sub-spiral, resembling Planaxis. The shells present 

 considerable extremes of form; and, if marine, might be easily referred 

 to Mesalia, Fusus, Bullia, Plcwiaxis, Litorina, and Drillia. Yet the 

 gradations between these extremes are so slight, and the differences in 

 the animals of such little importance, that the separation into natural 



froups is a matter of great difficulty. The shells are seldom attractive, 

 eing generally covered with a dull skin, and often with adhesive mud ; 

 many of them however are elegantly sculptured, and a few have very 

 graceful forms. It is much to be regretted that American collectors, 

 who have not been slow to avail themselves of the exuberant riches 

 lying at their feet, which are so acceptable to European naturalists, 

 have so generally entirely neglected the preservation and study of the 

 opercula ; and that so many points in the physiology and habits of these 

 easily-observed animals have not yet been made known. 



The shells of Melanid proper have a turreted spire ; oval mouth, with 

 sharp, straight lip. Like the Paludinas, they delight in the muddy 

 parts of rivers, but do not despise stony places. Many of the species 

 are said to be viviparous. In the section Melanella, the spire is 

 shortened ; and in Melacantlia, there is a coronet of sharp spines. These 

 are mostly found in the Old World and the Pacific islands. In Melana- 

 tria, which includes the finest East Indian forms, and many fossils of 

 the European tertiaries, the shell is strongly sculptured; the outer lip 

 is waved ; and the operculum has several whirls, with a central nucleus. 

 Pachycheilus, which includes many American forms, has a similar 

 operculum, with a smooth shell, and a thickened pillar-lip. The 

 stumpy, ridged CeripJiasia of the American rivers, and the stout, 

 nodulous Vibex of West Africa, agree in having the outer lip very 

 much waved, leaving a broad channel before and behind. Gyrotoma. 

 a North American form, has a lump at the back of the pillar, and a 

 deep, narrow slit at the suture. Very common in the whole district 

 west of the Alleghanies are the stumpy little Leptoxes (of Rafinesque ;* 

 Anculotus of Say) ; which are like fresh- water Periwinkles in their 

 habits. Having no tide-waves to dash them, they establish them- 

 selves on stones in the rapid places of rivers in such numbers that 



*The description is so inaccurate that Philippi in his Manual assigns it a plact- 

 among the Lymneids. The name of Say was in common use till the conchological archa>- 

 ologists revived the prior but deservedly forgotten name of Rafinesque. Changes of cur- 

 rency, however necessary to introduce the benefits of a decimal coinage, are not necessarily 

 useful to science, merely because a bad coin was made before a good one, which has got into 

 general acceptation. 



