NYMPHACEA. MOLLUSCA. SANGUINOLARIA. 65 



hairs, consisting of four large and four small ones ; and the same 

 number of short, obtuse points, without fringe, surround the orifice of 

 the other tube. 



PETRICOLA DACTYLUS. 



Shell elongated-ovate, chalky-white, very inequilateral, covered 

 with radiating lines and ribs ; no areola before the beaks ; teeth, two 

 in the right, and three in the left valve. 



FIGURE 41. 



State Coll., No. 245. Soc. Cab., No. 2327. 



Petricola dactylus, SOWERBY ; Genera, Petricola, f. 3. SAY ; Amer. Conch., pi. 

 60, f. 2. 



This shell very closely resembles the preceding, and will be 

 best described by a comparison with it. It has a more ovate 

 form, the basal margin being considerably arcuated ; the anterior 

 extremity is broader, and obtusely rounded ; there is no marked 

 areola before the beaks, but a deep depression under them ; the 

 ligament is longer ; the radiating lines are more numerous, the rib- 

 like anterior ones are more numerous (about sixteen), less ele- 

 vated, and the lines of growth merely undulate over them without 

 being raised into vaulted scales ; in the right valve are two teeth 

 similar to those in P. pholadiformis, but shorter and grooved ; in 

 the left valve, instead of the large, cleft tooth, we have two teeth, 

 the division between them answering to the cleft in the other 

 species ; the large middle tooth is folded, and the posterior one is 

 very slender. Length If inch, height f inch, breadth inch. 



Sent to me by Dr. L. M. Yale from Martha's Vineyard. 



It is a proportionally shorter and broader shell ; but its most obvious 

 mark of distinction is the want of an areola before the beaks. 



FAMILY NYMPHACEA, LAM. 



JVbf more than two cardinal teeth on the same valve ; nymph&, in general 

 externally prominent, and covered by the ligament. 



GENUS SANGUINOLARIA, LAM. 



.Shell equivalve, inequilateral, sub-ovate, compressed, rounded 

 anteriorly, sub-rostrate posteriorly, slightly gaping at sides ; hinge 

 9 



