FIST ULAN A. 373 



forated plate inserted at the bottom, analogous to the ter- 

 minal disc of the one that pertains to Aspergillum ; it is 

 surrounded with minute spiniform tubes, probably filled 

 also with certain fleshy filaments of the mantle. At the side 

 of the chambered end is imbedded the fixed valve, some- 

 what pearly in appearance ; and attached to the animal by 

 two strong muscles, is the corresponding valve, hinging 

 upon the other by a soft coriaceous ligament. 



In the genus Fistulana a different construction is ap- 

 parent. The bivalve shell is altogether free, and indepen- 

 dent of the tube in which it is confined, while the lower 

 end of the tube is inversely closed over. It consists merely 

 of two irregular, inequilateral valves, gaping widely at the 

 basal margin, and united by a soft ligament, and is en- 

 closed in the lower expanded cavity of the long, straight, 

 clavate tube, which it forms in the sand : the lower end is 

 closed, the upper open. 



The genus Gadrocliana has been removed from the 

 Pholadaria to the Tuhicola, because, like the rest of their 

 family, the animal lines the cavity, wherein he dwells, with 

 a shelly substance, and also forms an unconnected tube for 

 protection when not imbedded. The tube differs from that 

 of Fistulana^ in being often found in the open parts of 



