Boston Society of Natural Hitory. 389 



tica, parv& ; Cauda recurvata. Length .3 inch, breadth .08 inch. 

 Inhabits Dartmouth harbor, clinging to sea-weed. 



Difters from C. perversum, Lam., in the black sutural ridge, and in 

 the position of the middle series of granules ; and from Murex ad- 

 versus, Montagu, in its recurved canal, its distinct suture and its color. 



Mr. Couthouy concluded his paper on the Osteodesmacea, and also 

 instituted a new genus to include shells formerly embraced in genus 

 Anatina, but which, having a spoon-shaped hinge, are destitute of an 

 ossiculum. He thus characterized it. 



Genus Cochlodesma. 



Animal oval, compressed, enveloped in a thin mantle, closed by a 

 membrane in front, except at the anterior inferior extremity, where it 

 opens to give passage to a broad compressed foot, extending along 

 the whole inferior surface of the abdominal mass, which is inconside- 

 rable ; edges of the pallium thickened, and a little rugose ; siphons 

 long, slender, divided in their whole extent, and opening separately 

 into the branchial cavity. 



Shell transversely oval, thin and fragile, sub-equilateral, convexo- 

 depressed, slightly gaping at both extremities, inequivalve, right valve 

 more convex, beaks moderately prominent, inclining a little back- 

 wards, summits cloven and sub-nacrous posteriorly ; extremities 

 rounded. Ligament double, the external very slight and membra- 

 nous, the internal received into a horizontal, spoon-sliaped process on 

 each valve, supported by one or two divergent falciform costae, pro- 

 jecting from it obliquely and posteriorly; muscular impressions su- 

 perficial, remote, the anterior elongated-oval, the posterior small and 

 sub-triangular, united by a palleal impression profoundly indented pos- 

 teriorly. 



The Anatina Leana, Conrad, is the type of the genus; and the 

 Anatina prcetenuis, Turton, probably belongs to it. 



Mr. Couthouy then read descriptions of the following new species 

 of shells. 



NucuLA NAVicxjLARis. N. testa parva, laevi, fragili, ovali, sub- 

 sequilaierali, luteo-vireseente, antice rotundata, postice truncatula, 

 cardine dentibus octodecim, intus albo-nitescente. Length ii, height 

 ■£g, breadth -^^ of an inch. Inhabits Massachusetts Bay, vicinity of 

 Plymouth. 



Beaks more central and basal outline much more strongly curved, 

 than in N. myalis, Couth. 



Bulla lineolata. B. testa parvula, oblongo-ovata, ferruginea, 

 Iransversim oblique frequenterque striata, spira, prominula, apertura 

 magna, ad basim valde dilatata et sub-efTusS.. Length ^\, breadth 



