MALACOZOA. TROPIOrODA. LAMELLIBRANCHIATA. 221 



elliptical, convex, somewhat pellucid, very inequilateral, 

 nearly equally rounded at both ends. Gldber, smooth. 

 4. Montac&ta substridta. Shell ovate, semitrans- 

 parent, faintly striated concentrically, and marked with 

 obsolete radiating striulae. Substridtus, some what striated. 



GENUS 5. CORBULA. Shell very inequivalve, 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. Cdrbis, a twig basket. Bruguiere. 



1. Corbula ituequivAlvis. Shell rotundato-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>Aa?, dwelling in caverns. 

 Linnaeus. 



1. Ph6las 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. Phdlas cdndida. 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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