CONC11IFER A. 
453 
Section III.— Tenuipedes. 
The mantle barely united before; foot small, narrow, and 
compressed; shell having but a moderate gape. 
TRIBE I.-NYMPHACEA. 
Having never more than two primary teeth in the same valve ; 
shell frequently gaping at the lateral extremities; ligament ex¬ 
ternal ; umbones usually projecting outwards. The species are 
all littoral. 
* Without lateral teeth. 
Genus 30. — CRASSINA.— Leach.* 
Generic Character. —Suborbicular, transverse, equivalve, sub- 
inequilateral, close; hinge with two strong, diverging, primary 
teeth in the right valve, and two unequal ones on the other; 
ligament external, broader than long. 
Crassina Scotica. — The Scottish Crassina. 
Plate XC. fig. 3. 
Somewhat heart-shaped, a little compressed, with regular 
parallel grooves and ribs; impressions under the beak lanceolate ; 
covered with a yellow-brown epidermis; inside pure white; 
margin broad and plain. One inch long. Inhabits the Scottish 
and Devonshire coasts. 
Genus 31.—CAPS A.— Lamarck. 
Generic Character. — Transverse, equivalve, valves approxi¬ 
mate and close; with three primary teeth in the right valve, and 
a single bifid tooth in the left, inserted into a cavity in the op¬ 
posite one ; destitute of lateral teeth; ligament external. 
Capsa laevigata .— The Polished Cafsa. 
Plate XC. fig. 4. 
Triangular, subequilateral, obsoletely striated transversely; 
covered with a greenish-yellow epidermis ; inside violet towards 
the umbones. Two inches long. Inhabits the Indian ocean. 
* This genus was instituted by my ingenious friend Dr Leach, and com¬ 
municated by him to Lamarck, who adopted it, without acknowledging its 
having been pointed out to him by the Dr. 
