MOLLUSCA. • 75 



not well founded. It is adopted by most concliologists, althougli rejected 

 by Liiinoeus, Cuvier, and Blainville. 



This fiimily contains some of the most beautiful forms and finely colored 

 species, both in tint and pattern, among bivalve shells. There are upwards 

 of 1.50 living species, and the f jssil species are also numerous, and chiefly 

 found in the tertiary strata. There have been about sixty tertiary species 

 named from the formations of the United States. Yenus mercenaria is an 

 inhabitant of both coasts of the Xorth Atlantic, and is used for food. In the 

 markets of Philadelphia it bears the name of clam, and in Boston that of 

 cwaJiog. The colored margin of the shell was used by the aborigines in 

 the manufacture of their wampum. Cytherea dione {jjI. 77, Jig. 37) is 

 j'em ark able for its longitudinal sulcations, and the double rows of long 

 spines postei'iorly. 



Fam. 8. Crassatellidce. This family is represented by the genns 

 Crassatella, tlie mollusc of which being unknown, its affinities are doubtful. 

 There are about twenty recent species known, and a considerable number 

 of fossil ones, chiefly tertiary, but also cretaceous. Some authors place the 

 genus Astarte (also called Crassina) here, but Deshayes thinks the mollusc 

 (which is unknown) has an aflinity with Yenus. 



Class 2. Gastropoda. 



This class includes most mollusca with univalve shells, whether spiral or 

 not, as well as species without a shell. The head, absent in the Acephala, is 

 liere present ; and. on its presence Blainville's appellation of Parace])halophora 

 is founded, a character which is of more importance than the foot. 



Okder 1 . PoLYTHALAMiA. Tliis, the first systematic name applied to these 

 animals, was proposed by Soldani, 17S9. More recently they have been 

 studied by D'Orbigny, who is the chief authority upon them, and by 

 Dujardin. The original name is defective, and both these authors have 

 conferred French names upon them, in contemp>t of those rules which keep 

 nomenclature pure and uniform, names which are of no more account than 

 the German n?imii Bauclifdszler instead oi gasteropoda ', and should the 

 sj'stematic name be adopted subsequently to such a vernacular one, and be 

 a translation of it, the author of the latter cannot be quoted for the sys- 

 tematic name. 



These animals have been also named Foraminifera and Phizophoda. 

 Tlieir classification is difficult. Their shell bears a distant resemblance to 

 that of certain cephalop(.>da, and on this account they were for a considerable 

 period referred to this class. D'Orbigny considers them as a distinct class 

 betw^een the Echinodermata and Zoophyta, and Dujardin regards them as 

 acalephse, and as allied to infusorial forms like Amiba and DIffiugia, Agassiz 

 regards them as the lowest form of the gasteropodous mollusca, and we 

 place them provisionally here, although they seem to have neither head nor 

 foot, two important organs in this class. The apparent want of viscera 

 indicates a position below that of the Bryozoa, and although the locomotive 

 organs may be assumed as giving them a higher position, these are probably 

 merely a modification of the tentacles. 



