SPH^RIIDM, 



FAMILY I.-SPH-ffiRIID-ffi. 



Body somewhat globular ; mantle produced (lengthened) in 

 front into either one or two siphons or tubes, which the animal 

 has the power of extending or contracting. In those species 

 which are furnished with two siphons, the longer one serves for 

 breathing and nutrition, the other for excretion ; the edges of 

 the mantle and tubes are simple, that is, they are not provided 

 with filaments ; foot wedge-shaped, exceedingly extensile. 



Shell with two valves, which are of equal size, but more or 

 less inequilateral, and of an oval or subtri angular form ; hinge 

 furnished with cardinal and lateral teeth ; ligament placed at the 

 posterior (hinder) side of the hinge, external, but sometimes 

 nearly hidden. 



The SphcsriidcB dififer from most of the Gondii fera 

 in having their siphons placed in front instead of at 

 the posterior end. They are active in their habits 

 and frequently float on the under surface of the water 

 with their foot spread out upon it, the shell at the same 

 time being inverted ; in addition to this, many if not 

 all of the species have the power of spinning gela- 

 tinous threads by means of which they raise and 

 lower themselves, or remain suspended in the water. 



They feed on animalcula, and in winter bury them- 

 selves in the mud, where they remain in a torpid state 

 until the return of spring. 



They are ovoviviparous, that is, the eggs are 

 hatched and the living fry retained for a time within 

 the body of the parent before they are born. 



GENUS L—SPH.E'RIUM* SCOPOLI. 



Body, sides nearly equal ; ma7ttle with two siphons (or tubes), 

 which are placed in front. 



Shell nearly equilateral ; beaks almost central. 



* A sphere or globe. 



