MOLLUSCS. 277 



England made their purple wampum, or suckauhock, which was regarded as twice as 

 valuable as the white money, or wompom proper. This latter was made from various 

 shells, but mostly from Jiusycon. 



Many other species of Venus, in its broader sense, are found in the warmer seas of 

 the world, the west coast of America being better supplied than the east. 



Cytherea and its sub-genus Caltista are readily distinguished from Venus by the 

 presence of an anterior lateral tooth in the left valve, which fits into a corresponding 

 depression in the other. Like the last genus it is rich in species, especially in the 

 warmer seas of the world. Our northern C. convexa has an outline much like that of 

 the quahog, but its dead white surface does not render it as attractive as its southern 

 relative, Gallista gigantea, which is found on our southern coasts. Cytherea lusoria 

 is a Chinese species, which derives its specific name from the fact that the inhabitants 

 of the celestial empire jjaint certain figures on the inner surface of the valves, and 

 then employ them in some of their many games of chance. Cytherea scripta has a 

 ground of white or yellow, over which is laid a series of zig-zag reddish-brown lines, 

 which require a rather vivid imagination to be regarded as resembling writing. It 

 comes from the Indian Ocean, as does the C. erycina. C. dione, from the west coast 

 of America, is a remarkable species, from the fact that it is ornamented by a series of 

 long slender spines, running in a row down the i^os- 

 terior side of the shell, from the umbones to the mar- 

 gin. The color is a rosy purple, varying considerably 

 in depth. In the more recent systems of classification 

 it is made the type of the genus Dione. 



Meroe embraces a few species of oval shells, with 

 three cardinal teeth and a long anterior tooth. The 

 general shape can be seen from our figure, but there is 



nothing of popular interest to be said concerning the fig. 297.— Jferas. 



species. Dosinia is represented on our shores by a 



species (D. discus), the specific name of which is very apt. The shell is flat, and 

 nearly circular in outline ; the siphons are united, and the foot is large. 



Gemma embraces only a single species, found on our coast, and known under the 

 repetitive name of Gemma gemma. In size it is minute, scarcely more than an eighth 

 of an inch in length, and in color it is a yellowish white, or rosy, tipped posteriorly 

 with an amethystine purple, so that the name is very appropriate. It would appear 

 that it was known to the early settlers of this country, and that they sent specimens 

 of it, along with other curiosities, to the old world ; and yet it was imknown to natu- 

 ralists until the year 1834, when the eminent engineer, General Totten, who was a 

 good naturalist withal, published a description of it. It is an active species, found on 

 sandy shores, where it burrows quickly. One of the most interesting facts known in 

 connection with it is that it retains the young inside its valves until the shells are fully 

 formed, sometimes thirty young being found inside of the parent shell. 



N"© species of the genus Tapes occur on our coasts, but the seas of other parts of 

 the globe contain nearly a hundred species. The shells are long, the siphons separate 

 at their extremities, and the long, slender foot spins a byssus. Many of the species 

 are ornamented with zig-zag lines, of darker color, and in Europe, especially on the 

 Mediterranean coast, T. geographica is used as an article of food. 



The family Peteicolid.<e is a small one, and its only member which requires men- 

 tion is the form known as Petricola pholadiformis. This is a thin, long shell, orna- 



