MALAC0ZOA. TEOPIOPODA. LAMELLIBRANCHIATA. 221 



elliptical, convex, somewhat pellucid, very inequilateral, 

 nearly equally rounded at both ends. Gldber, smooth. 

 4. Montacuta substridta. — Shell ovate, semitrans- 

 parent, faintly striated concentrically, and marked with 

 obsolete radiating striulae. Substridtus, somewhat striated. 



Genus 5. Corbula. — Shell very inequi valve, inequi- 

 lateral, little gaping ; right valve with the umbo promi- 

 nent ; hinge with a curved pointed tooth and a cavity in 

 the right, and a spoon-shaped tooth in the left valve ; 

 ligament internal. Corbis, a twig basket. Bruguiere. 



1. Corbula inaquivalvis. — Shell rotuudato-trigonal, 

 very inequivalve, concentrically striato-sulcate, the 

 smaller valve with radiating lines. Incequivalvis, having 

 unequal valves. 



Family XII. — Pholadina. 



Animal having the mantle closed and more or less 

 tubular, with an anterior aperture for the foot, which is 

 small, and two elongated coherent tubes ; the branchiae 

 elongated, extending into the siphon. Shell generally 

 bare, white, brittle, open at both ends, with the hinge 

 toothless, the ligament external, often with a calcareous 

 plate. Name from the genus Pholas. 



Genus 1. Pholas. — Shell oval or oblong, equivalve, 

 inequilateral, thin, white, open at both ends ; hinge 

 furnished with accessory plates ; a curved calcareous 

 process under the umbo. $a>\as, dwelling in caverns. 

 Linnaeus. 



1. Phdlas crispdta. — Shell subovate, widely open at 

 both ends, convex, angulate before, with a ridge from 

 the umbo to the lower margin. Crispdtus, marked with 

 undulated laminae. 



2. Pholas Candida. — Shell ovato-oblong, less open at 

 the anterior end, convex, thin, with radiating elevated 

 lines decussated by concentric lines. Cdndidus, white. 



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