THE BIVALVES 3389 



namely, the Poromyidce and Cuspidariidce. Of the former, Poromya has the 

 siphons short, unequal, separate, and surrounded by a tentacular fringe; each 

 half of the septum having several groups of lamellae, separated by orifices; the 

 foot being slender, long, and the palpi larger. The shells are often minutely 

 granular and somewhat pearly within. The species are small, few in number, 

 and mostly from very deep water. Silenia is a deep-water form, dredged in one 

 thousand nine hundred and fifty fathoms, about eleven hundred miles southwest of 

 Australia, and also in the South Atlantic at the enormous depth of two thousand 

 six hundred and fifty fathoms. The Cuspidariidce is a more extensive family, and 

 although the species are nearly all small, some are elegant in form, and prettily 

 sculptured. The shells have been classified by characteristics derived from modifi- 

 cations of the hinge, and the surface ornamentation. The siphons are longer 

 than in the PoromyitUe and united with tentacular fringes at the ends; the 

 foot is moderately long and pointed, the labial palpi are rudimentary or wanting, 

 and the branchial septum is pierced with isolated symmetrical orifices. The shells 

 are mostly transversely ovate, and produced posteriorly into a more or less elongate 

 rostrum. They are found in all seas, in depths ranging from a few fathoms to over 

 three miles. 



