298 



POPULAR CONCHOLOGY. 



Byssanodonta. UOrb. — Shell roundish, oval, thin, 

 equivalve, closed ; the pallial impression entire ; two 

 muscular impressions, the front one small, transverse, not 

 lobed, and the larger under one more oblique ; a linear 

 outer ligament ; hinge toothless. Animal, having an open 

 mantle, and a rudimentary foot with a byssus. — 1 species. 



B. Paranensis, a small shell, is from the rivers of 

 Panama. 



Modiolopsis. Hall. — Shell equivalve, inequilateral, 

 lengthened, broader behind, the bosses lie near the front 

 extremity; furnished with a single strong muscular im- 

 pression like Modiola (?) often a sinus extending from the 

 front side of the boss to the hinder, so that the front part 

 is drawn into a kind of lobe. — 16 species, fossil. 



The shell is thin, and the surface has fine concentric 

 strise. 



Hippopodium. Conybeare. — Shell equivalve, obliquely 

 transverse, heavy, deep, inequi- 

 lateral, umbones incurved ; ven- 

 tral margin sinuated so as to 

 give a bilobed appearance to the 

 shell ; hinge incrassated with 

 one rugged oblique tooth.* — 

 Fossil. 



A large heavy fossil shell, with 

 the bosses much incurved, and behind them a deep heart- 

 shaped cavity. 



Hippopodium ponderosum. 



Family 2.— FINN ACE A. 



The mantle of the animal is entirely cloven, and there 

 is no distinct tube behind ; the edo-e is beset with cirrhi ; 



* Sowcrby's Couch. Manual. 



