﻿UNITED STATES. 01 



towards the margin ; cardinal teeth small, compressed, striate, double in both valves ; 

 lateral teeth very long, lamellar and nearly straight, single in the right and double in 

 the left valve ; anterior cicatrices distinct and rather deeply impressed ; posterior 

 cicatrices large and confluent ; dorsal cicatrices small and placed above the centre of 

 the cavity of the beaks ; cavity of the shell shallow ; cavity of the beaks very shallow 

 and rounded ; nacre purple or salmon and iridescent. 



Soft Parts. — Branchial uterus not changed in any of the six under examination ; 

 some had ova in the ovarium. Branchim very wide, gently curved below, the inner 

 ones very much the larger, free two thirds the length of abdominal sack. Palpi 

 rather large, subangular, united halfway down the posterior edges. Mantlevery thin, 

 slightly thickened at the margin. Branchial opening rather large, with small light 

 brown papilla} on the inside of the edges. Anal opening rather large, with very indis- 

 tinct crenulations on the edges. Super-anal opening large, edges not colored, united 

 below for some distance. Color of the mass whitish. 



Remarks. — This belongs to the complanatus group, and is between Tuomeyi (nobis) 

 and complanatus. It is more oval than the latter and not so oblique as the former- 

 In outline it is near also to U. vicinus (nobis). Nearly all the specimens which have 

 come under my notice have a small ventral cicatrix. I have not seen any young 

 individuals, nor adults, with perfect beaks, but presume that the undulations of the 

 tips will be found very much like those of complanatus. 



Unto vicinus. PI. 9, fig. 43. 



Testii laevi, oblonga, compressa, insequilaterali ; valvulis subcrassis ; natibus prominulis ; epidermide virido- 

 fusca, obsolete radiata ; dentibus cardinalibus parvis, acuminatis compressisque ; lateralibus longis sub- 

 curvisque ; margarita argentea et valde iridescente. 



Shell smooth, oblong, compressed, inequilateral ; valves rather thick ; beaks a little 

 prominent; epidermis greenish brown, obscurely radiated; cardinal teeth small, 

 pointed and compressed ; lateral teeth long and somewhat curved ; nacre silvery and 

 very iridescent. 



Proc. Acad. Nat. Sci. 1856, p. 262. 



Hob. — Swift Creek, near Macon, Georgia. Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. -7, Length 14, Breadth 2-6 inches. 



Shell smooth, oblong, compressed towards the middle and the basal margin, subangu- 

 lar behind and raised on the posterior slope quite into a keel ; substance of the shell 

 rather thick ; beaks a little prominent ; ligament rather long and thin ; epidermis 

 greenish brown, with obsolete rays, shining on the umbones, with very distant marks 

 of growth ; cardinal teeth small, pointed, compressed, striate, single in the right and 

 double in the left valve ; lateral teeth very long, lamellar and slightly curved ; anterior 

 cicatrices distinct ; posterior cicatrices rather large and confluent ; dorsal cicatrices 



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