MOLLUSCA. "5 
not well founded. It is adopted by most conchologists, although rejected 
by Linneeus, Cuvier, and Blainville. 
This family contains some of the most beautiful forms and finely colored 
species, both in tint and pattern, among bivalve shells. There are upwards 
of 150 living species, and the fossil 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. Venus mercenaria is an 
inhabitant of both coasts of the North Atlantic, and is used for food. In the 
markets of Philadelphia it bears the name of clam, and in Boston that of 
cwahog. ‘The colored margin of the shell was used by the aborigines in 
the manufacture of their wampum. Cytherea dione (pl. T7, jig. 37) is 
remarkable for its longitudinal sulcations, and the double rows of long 
spines posteriorly. 
fam. 8. Crassatellide. This family is represented by the genus 
Crassatella, the 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 affinity with Venus. 
Class 2. Gastropoda. 
This class includes most mollusca with univalve shells, whether spiral or 
not, as well as species without ashell. The head, absent in the Acephala, is 
here present; and on its presence Blainville’s appellation of Paracephalophora 
is founded, a character which is of more importance than the foot. 
Orver 1. Potryrnanamta. This, the first systematic name applied to these 
animals, was proposed by Soldani, 1789. 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 snthor have 
conferred French names upon them, in contempt of those rules which keep 
nomenclature pure and uniform, names which are of no more account than 
the German name Berebancles instead of gasteropoda ; and should the 
systematic 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 Rhizophoda. 
Their classification is difficult. Their shell bears a distant resemblance to 
that of certain cephalopoda, and on this account they were for a considerable 
period referred to this class. D’Orbigny considers them as a distinct class 
between the Echinodermata and Zoophyta, and Dujardin regards them as 
acalephee, and as allied to infusorial forms like Amiba and Difflugia. 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 
shenéhy a modification of the nein. 
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