CONCHIFERA: 



311 



readily break to pieces from the vertical arrangement of 

 the fibres, and it is supposed they were equally brittle 

 when recent. 



Pulyinites. Defiance. — Shell subequivalve, inequi- 

 lateral, compressed, thin, slightly gaping posteriorly ; one 

 valve flat, the other rather concave ; hinge linear, short, 

 divided into perpendicular grooves ; muscular impressions 

 two*, one subcentral, the other above it near the hinge. f 

 —Fossil. 



Very like Melina (Perna), the only species is P. Adan- 

 sonii. 



Pachymya. Sow. — Shell obliquely elongated, equi- 

 valve, thick, sub-bilobed, with beaks near the anterior 

 extremity ; ligament partly immersed, attached to promi- 

 nent fulcra, f — Fossil. 



Shaped like Modiola ; a large heavy fossil shell from 

 Lyme Regis, called P. gigas. 



Family Z.—PECTINACEA. 



These animals have a foot, though it is sometimes little 

 developed ; most of them have a byssus ; the mantle lobes 

 are completely separated, and the edge furnished with 

 numerous tentacula and eyes. The shell is mostly in 

 equivalve, but regular, not foliaceous, but porcellaneous ; 

 with two ears at the hinge, which is straight, with or 

 without teeth, and the ligament is in a triangular pit, or in 

 a channel which extends to the bosses. Found in the sea 

 in all zones. 



Pedum. Brug. — Shell irregular, longitudinal, or hatchet- 



* Philippi says they are unknown, 

 t Sowerby's Conch. Manual, 

 x 4 



