74 ZOOLOGY. 



clouded with violet, and the pallial impression curved. The older authors 

 placed it under Venus and Tellina. It inhabits Junk river and other 

 rivers of west Africa near the mouth,* 



Glaucomya of Gray belongs here. Mr. Cuming found it living in the 

 fresh watere of the Philippines, and it occurs fossil in the freshwater forma- 

 tions of Paris. It was at first confounded with Venus. 



Fain. 5. Tellinida; (also named Nyniphacea). In this family the cardinal 

 and accessory teeth are well developed, the shells are seldom covered with 

 u periostraca, the mantle is margined with very sensitive tentacular 

 appendages, and closed posteriorly, the siphons ai*e exserted, and the pallial 

 impression has a deep sinus. 



Dowix {pi. 70, figs. 38, 39) has a wedge-shaped shell, truncated upon 

 the posterior slope, making this extremity unusually short. Some authors, 

 as Swainson, have mistaken the posterior for the anterior extremity, 

 although the short ligament and the curve in the pallial impression should 

 have prevented such an error. Donax is a genus of handsome and usually 

 small shells, al)undant in individuals, and living vertically in the mud at a 

 trifling depth of water. A few species are found in tertiary formations. 

 Capsa includes shells allied to Donax, but without accessory teeth. 



Tiilina {pi. 7G,fig. 44) is a genus of handsome and usually elongated 

 shells with a fine nacre, often polished and radiated externally, and in some 

 cases rough. The recent species are numerous, and there are a considerable 

 number of fossil species in the tertiary of Europe and America. 



Blainville places Amphidesma as a section of Lucina ; Latreille considers 

 it the representative of a family; and Deshayes thinks it has characters 

 intermediate to Mactra and Tellina, to the latter of which he surmises that 

 the unknown animal is allied. 



Fam. 6. Liicinidw.. This family is sometimes united to the Tellinidse. 

 Lucina presents some important distinguishing characters. The shell is 

 suborbicular, white or pale colored ; the labial palpi are absent, the branchiae 

 of each side are united so as to appear single, although separable ; the foot 

 is vermiform, and there is a single anal siphon capable of being turned 

 within itself like the finger of a glove. The branchial siphon is reduced 

 to a simple perforation. The genus has numerous species, recent and fossil 

 in the tertiary formations. 



Fam. 7. Veneridm. This family contains the extensive genera Venus 

 {pi. 76, fig. 36) and CytTierea {fig. 37), and also Arthemis of Poli. The 

 species of Venus and Cytherea being numerous, the accessory tooth which 

 «listinguishes the latter is found more or less developed, and as it is at times 

 reduced to a mere vestige, Deshayes is inclined to consider the genus as 



* Magadesma of Bowditch was probably published in his treatise on Conchology. It was 

 named Galathea by Bruguieres, a name which has been already used. Sowerby called it 

 Potamophila, and De Roiasy Egeria, a name which occurs three times in Entomology, being 

 instituted by Dumeril in 1806, Fabricius in 1808, and Desvoidy in 1830. Leach used it in 

 1815 in the Crustacea, and Lea in 1833 in the Mollusca. The constant use of Agassiz' important 

 and laborious Nomexclator Zoologicus (containing 33,000 names of genera, <fec.) can alone 

 prevent such confusion. 

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