100 INVERTEBRATA OF MASSACHUSETTS. 



NUCULA SAPOTILLA. 



Shell elongated-ovate, sub-equilateral, sub-rostrated, tumid at 

 the beaks, with a slight flexure under the posterior tip, pale yellow- 

 ish-green, polished ; teeth about sixteen on each side. 



Figure 61. 



State Coll., No. 182. Soc. Cab., No. 2338. 



Shell ovate, prolonged, thin, fragile, translucent, the beaks a 

 little in advance of the centre, not elevated, but considerably in- 

 flated laterally ; anterior half regularly semi-oval ; posterior por- 

 tion narrowed and compressed, the line running from the beaks to 

 the posterior tip straight, and rendered sharp by the compression 

 of a very narrow portion of the margin ; beneath the tip is a trun- 

 cation or shallow indentation of the margin, bounded by a wave- 

 like swell passing from the beaks to its anterior termination ; 

 surface marked only by exceedingly minute concentric lines, and 

 covered by a very thin and glossy epidermis of a light yellowish- 

 green color, with an occasional narrow zone of a darker color ; 

 within pearly-white ; cavity of the cartilage deep and triangular ; 

 teeth about sixteen or eighteen on each side, long and pointed, 

 very small and crowded at the centre. Length j\ inch, height f 

 inch, breadth y^^- inch. 



Inhabits the vicinity of Cape Cod, where it may be found in 

 the stomachs of fishes, and also by dredging. Many specimens 

 have been kindly furnished me by Colonel Totten, which he took 

 by dredging in Provincetown harbour. 



This is the living analogue of the fossil species described by Mr. Say 

 under the name of N. Icbvis, in " American Conchology," pi. 12. In 

 size, shape, and the position of the beaks they accurately agree ; but 

 the fossil species wants the emargination or flexure under the posterior 

 tip. N. myalls is greater in height, thicker, darker, and has the beaks 

 about as far removed towards the posterior as they are towards the 

 anterior extremity in this shell. 



Eroded spots, filled with a black substance, are frequendy seen ex- 

 ternally, which are marked by a corresponding chalky opacity within. 



