92 THE NAUTILUS. 



THE SHELL-BEARING MOLLUSCA OF RHODE ISLAND. 



BY HORACE F. CARPENTER. 



The earlier portion of this paper appeared in Volumes III. and IV. of this 



Journal.] 

 199. Toldia sapotilla Gould. 



Nucula sapotilla Gld., DeKay, Sby., Hanley ; Leda sapotilla 

 Stimp., S. I. Smith, Reeve ; Toldia sapotilla, of modern authors. 



Shell elongated ovate, thin, fragile, translucent ; beaks nearly 

 central, a little nearer the anterior end, not elevated ; anterior por- 

 tion of the shell semi-oval, regularly rounded, posterior narrowed and 

 compressed but not so much so as in T. limatula ; surface with very 

 minute concentric lines ; epidermis thin, glossy, bright yellowish- 

 green with one or two narrow zones of a darker shade ; interior 

 white and pearly ; hinge with sixteen long and pointed teeth on each 

 side of the beaks, those near the center small and close together. 

 Length T %, height |, breadth T ff inch. 



This species is comparatively rare and local, but inhabits soft mud 

 in deep water from Long Island to the Arctic Ocean. It has been 

 dredged in Provincetown Harbor by Col. Joseph G. Totten, and in 

 Long Island Sound by Mr. S. Smith. Prof. A. E. Verrill has 

 dredged it off Gay Head, 19 fathoms; Buzzard's Bay, 25 fathoms; 

 east of Block Island, 29 fathoms ; and in Casco Bay and Bay of 

 Fundy, 4 to 100 fathoms. Quoted from Mass. Bay (Gould), Nova 

 Scotia (Willis), Labrador (Packard), Greenland (Morch). 



Gould says, " In its shape and the perfect polish of its surface, 

 this shell resembles the seed of the Sapotilla (Ackras sapota), a trop- 

 ical fruit," and for this reason he gave it its specific name. 



Toldia obesa Stimp. and Toldia thraciformis Stimp. have been 

 quoted from Long Island to Greenland, but have not as yet been 

 found in Rhode Island. 



Family Arcidje. 



The Arks are boat- shaped shells, having a straight hinge with 

 numerous short comb-like teeth ; the umbos separated from each other 

 by a flat, lozenge-shaped ligamental area, and on the interior of the 

 valves are two distinct muscular impressions. The animals have two 

 hearts, each with an auricle ; they spin a byssus not like the mussels, 

 but a horny substance composed of numerous thin calcareous plates 



