DREISSINA. 147 



Mr. Eeeve's Monograph contains fourteen species. Dolium 

 Maculatum. PI. xix. fig. 420. 



DONAX. Linnffius. Fam. Nymphacea, Lam. Conchacea, Bl. — 

 Descr. Equivalve, inequilateral, trigonal, with the anterior side 

 short, straight, plane ; the posterior side elongated, drawn to a 

 narrow, rounded termination ; hinge with two cardinal teeth in 

 one valve, one in the other, and one or two, more or less remote 

 lateral teeth ; ligament external ; muscular impressions two in 

 each valve ; palleal impression sinuated posteriorly. — Obs. The 

 Capsae have not the crenated margins, the short anterior side, 

 and the distinct lateral teeth, which characterize the Donaces. 

 Some species of Erycina resemble Donax in general form, but 

 are at once distinguished by the ligamentary pit in the hinge. 

 The Donaces inhabit sandy shores in all climates. D. cuneatus. 

 PI. V. fig. 108. 



DOESAL. A dorsal shell is one placed upon the back of the ani- 

 mal. The dorsal margin of a bivalve shell is that on which the 

 hia^ is placed ; the opposite margins are termed ventral. The 

 dorsal surface of a spinal univalve is that which is seen when the 

 aperture ia turned from the observer. The dorsal valve is the 

 uppermost in Brachiopodous bivalves. The dorsal part of a 

 symmetrical convolute univalve, such as the Nautilus and Am- 

 monite is that part of the whorls which is at the greatest dis- 

 tance from the spire, that is, the outer part of the whorls. Thus 

 the situation of the siphon is said to be dorsal when it pierces the 

 septum near the outer edge of the whorls. The dorsal part of 

 symmetrical conical univalves, such as Patella, is the upper part, 

 on which the apex is placed. 



DOESALIA. Lam. {Dorsum, the back.) The first family of the 

 order Ann elides Sedentaria, Lam. containing the genera Areni- 

 cola, not a shell, and Siliquaria, fig. 1, which is now considered 

 as a true moUusc, and placed next to Yermetus. 



DOSINA. Schum. Venus Verrucosa, Casina, and similar spe- 

 cies. Pig. 119, a. 



DEEISSINA. 1835. Mttilfs Polymorphus. Auct. fig. 159. 

 This genus difiers from MytUus principally in the characters 



1 2 



