CONCHIFERA. 



281 



sus ; lips formed of a linear prolongation of the branchial 

 lamina?. — 52 species * ; also fossil. 



The Pectunculus is found in the West Indies, Atlantic 

 Ocean, and Mediterranean, where it lives on the sandy or 

 muddy coasts, and moves by means of its foot. Many 

 of the species have a soft downy epidermis, but no byssus. 

 P. glycimeris is the British species. The fossil species 

 are numerous, and some occur in immense numbers, Dr. 

 Mantell says that in the limestone at Bognor he has seen 

 fifty specimens lying in relief on an area of a foot square. f 



LiMOPSrs. Sassi. (Trigonocaelia Nyst.) — Shell sepa- 

 rated from Pectunculus because the hinge plate has a 

 separate triangular pit, the point reaching up to the boss, 

 for the ligament. Animal unknown. — Few species ; also 

 fossil. 



The living species are not much known. 



Family 17. —NUCULACEA. 



The animal has the mantle either entirely open, or 

 closed behind and prolonged into two short, or long 

 siphons ; gills leaf-shaped ; the mouth tentacles very 

 large, and placed very backward; foot large, the basal 

 surface can often be folded together; no byssus. The shell 

 is triangular, or transverse ; the small bosses touching, with 

 no flat space as in Area ; the hinge linear, forming an 

 angle, and beset with numerous pointed teeth ; ligament 

 internal. — Marine ; found in most seas. 



Nucula. Lam. (Polydonta Megerle.) — Shell varying 

 in shape, equivalve, inequilateral ; teeth small, numerous, 



* Reeve's Icc-nica, 



f Medals of Creation. 



