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2 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.75 



The muscle scars of both shells are identical, forming shallow cica- 

 trices on the interior face of the shell. The anterior adductor scar 

 lies in front of the pseudocai'dinal teeth and is somewhat oval in 

 outline. At the termination of the lower pseudocardinal tooth is 

 the anterior retractor muscle scar which is deeper than the anterior 

 adductor scar and continuous with it. Below the impression of 

 these two muscles is the small circular impression of the protractor 

 pedis muscle. At the termination of the lateral hinge tooth is the 

 scarcely visible oval scar of the posterior adductor muscle. Directly 

 above it is the impression of the posterior retractor muscle which is 

 small and circular and often invisible. A very faint line runs about 

 a quarter of an inch from the margin of the shell from the anterior 

 to the posterior adductor muscle. It is the impression of the pallial 

 line muscles, small muscles inserted along the margin of the mantle. 



In the beak cavities there is an irregular number of very small 

 scars, one of which is a deep elliptical scar in the apex of the cavity 

 and is the impression of a small dorsal mantle muscle. 



UANTLE 



Plate 1, fig. 3 



The mantle lobes are separated for almost the length of the poste- 

 rior adductor muscle in the formation of the dorsal mantle aperture. 

 They are then united for about 3 mm. before separating to form the 

 exhalent siphon. The tentacles of the exhalenl siphon are rudi- 

 mentary while those of the inhalent siphon are from 1 to 2 mm. in 

 length. 



The pigmentation of the dorsal mantle aperture and of the siphon 

 is heavy, growing fainter and disappearing as the margins continue 

 anteriorly. 



The lack of pigmentation along the entire mantle edge, exclusive^ 

 of the siphons, the absence of tentacles beyond the inhalent siphon 

 but rudimentary tentacles at the exhalent siphon and a more elon- 

 gate form of body distinguish this species from L. nasutus. 



MUSCULAR SYSTEM 



Plate 1, fig. 8 



The largest muscles are the anterior and the posterior adductor 

 muscles, great cylindrical masses of fibers situated on a line with 

 each other on the dorsal portion of the body, piercing the mantle as 

 they traverse the body to their attachment on the valves. Their 

 functioning keeps the valves closed. 



The remaining muscles are the anterior and the posterior retrac- 

 tors, the protractor pedis, two small muscles inserted in the cavities 

 of the beak, and the small muscles of the pallial line. In alcoholic 

 specimens, the anterior retractor muscle is very small and circular 

 in appearance, with its point of insertion just posterior to the upper 



