CORBIS. DIMY ARIA. 105 
is situate anteriorly ;* but in most of the species a small portion of the liga- 
* ment is likewise placed behind the beaks, The shells of this genus are for the 
most part wedge-shaped. 
Some species of Erycine may be mistaken for Donaces, but the ligamentary 
pit in the hinge of the former genus, will at once distinguish it from the latter ; 
the Capsz have also a strong resemblance to this genus, but are always devoid 
of the short anterior side, and crenated margins which characterize the 
Donaces. 
The Donaces inhabit the Ocean. Fossil species are few and rare. Brocchi 
mentions only two, and Sowerby one from Bordeaux. 
Genus XXXIV, — LUCINA. — Bruguiére. 
Generic Character. — Shell equivalve, inequilateral, 
usually orbicular, lenticular, and subdepressed ; teeth 
variable, most commonly two minute cardinal teeth, diver- 
gent from the umbo, frequently nearly obsolete ; in one 
valve one lateral tooth on each side of the umbo, and ‘two. 
on each side in the other ; the anterior lateral ones being 
situate near the primary teeth, and the posterior imme- 
diately behind the ligament: two muscular impressions 
remote from each other, the anterior one generally extruded 
backwards and downwards in the form of an elongated 
band ; pallial impression destitute of a sinus; ligament ex- 
ternal, elongated, and partly hidden by the inflected mar- 
gins of the valves when closed, consequently, the internal 
tendinous portion is frequently sunk into a deep, elongated 
cavity, situate between the teeth and hinge-margin. 
Lucina mites. Plate IX. fig. 25. 
Although the general form of the Lucinz is lenticular, they are subject to 
considerable variety; some species,—the L. Columbella for example, is 
nearly globular. The teeth also differ considerably in number and size, but 
never in position ; some species have cardinal teeth only, while in others the 
lateral are more distinct than the cardinal teeth; in a few species both are 
considerably developed, and in others they are all nearly obsolete. 
The Lucinz have much of the general aspect of the Amphidesme, but are 
distinguished by their anterior muscular impression being ligulate; the 
Amphidesmz have a very large sinus in the muscular impression in the 
mantle, and the tendinous part of the ligament entirely internal. This ligu- 
late muscular impression distinguishes them from the Cytheree. 
The Lucine inhabit the ocean. Fossil species are numerous, and occur in 
the beds of the Tertiary formations, of which they are a characteristic type. 
Genus XXXV.— CORBIS. — Cuvier. 
Generic Character. — Shell transverse, equivalve, free, 
oval, thick, extremely ventricose and subequilateral ; um- 
* Contrary to Lamarck, we consider the side in which the ligament is situate, to be the 
anterior side, and it are only lead to confusion to make an exception in this genus. 
