116 PROVISIONAL AID TO THE STUDY OF TASMANIAN MOLLUSCA. 



(xcviii.) Family PECTiNicas. 

 Genus Pecten. (702-706.) 

 Shell sub -orbicular, regular, resting on the right valves, usually- 

 ornamented with radiating ribs; beaks approximate, 

 eared ; anterior ears most prominent ; posterior side 

 a little oblique ; right valve most convex, with a notch 

 below the front ear; hinge margins straight, united 

 by a narrow ligament ; cartilage internal, in a central 

 pit ; adductor impressions double, obscure ; pedal 

 impression only in the left valve, or obsolete. Dist. — 

 World-wide, Nova-Zembla, Cape Horn j 200 fathoms. 



(xcix.) Family Tjuuxdm. 

 Shell eared, white, gaping at the sides; hinge edentulous, 

 with a central, triangular cartilage-pit. 



Genus Lima. (707-708.) 

 Shell equivalve, compressed, obliquely oval ; anterior side 

 straight, gaping, posterior rounded, usually close ; 

 umbones apart, eared ; valves white, smooth, punctate, 

 striate, or radiately ribbed and imbricated ; there is 

 usually a thin, brownish epidermis ; hinge-area tri- 

 angular, cartilage-pit central; adductor impression 

 lateral, large, double ; pedal scars two, small. Dist. — 

 Norway, Britain, West Indies, Canaries, India, Aus- 

 tralia, 1-150 fathoms. The largest living species (L. 

 excavata, Chemn) is found on the Coast of Norway. 



(c.) Family Anomiid2e. 

 Genus Placttnanomia. (709.) 

 Shell adherent, sub-equivalve, irregular, flattened, ; hinge with 

 two thick divergent elongated lamella in the inferior, 

 corresponding with two long pit in the upper valve ; 

 upper valve with only two muscular impressions, the 

 pedal scar radiately striated ; the byssal plug is often 

 fixed in the lower valve, and its muscle becomes 

 (functionally) an adductor. Dist. — West Indies, 

 Britain, New Zealand, California, Behring's Sea, 

 Ochotsk ; 50 fathoms. Mocine, California. P. 

 macrochissna, Desh. 



(ci.) Family Osteeid^e. 

 Genus Ostrea. (701-713.) 

 Shell irregular, attached by the left valve ; upper valve fat or 

 concave, often plain ; lower convex, often plaited or 



