No. 104.] 163 



in imagination, by twisting a solen, so that the ventral and dorsal 

 margins formed a complete turn of a spiral; but the beaks are in the 

 middle of the anterior extremity, and other characters are incompat- 

 ible with a solenoid shell. Its form suggests Parallelopipedum, but it 

 is evidently not an Area. In its reflexed and minutely plicate margins 

 and absence of proper hinge, it resembles some forms of Pholas, and, 

 in addition, its spiral form is strongly indicative of a burrowing habit. 

 Further, the small mass of rock containing the specimens of S. insigtiis, 

 preserves the remains of several individuals, showing that they were 

 gregarious after the manner of other burrowing shells. 



The twisted form of the shell and the position of the muscular scars 

 precluded any considerable opening of the valves by the animal; and 

 the shape of the anterior end shows that there could have been no well- 

 developed foot for locomotion. Taking all these features into con- 

 sideration, it seems evident that in this genus, we have a farther addi- 

 tion to the interesting group of boring mollusca. 



