Lima.] PELECYPODA. 887 



Diameter Ant. -post., 4-5 mm. ; dorso- ventral, 7-1 mm. : thickness, 

 3-5 mm. (W. H. Ball.) 



Type in the U.S. Nat. Museum, Washington (No. 195290). 



Hob. Port Pegasus, Stewart Island, in 18 fathoms, type (Captain 

 Bollons) ; Foveaux Strait, in 15 fathoms ; Snares, in 50 fathoms 

 (Captain Bollons). 



Fam. OSTREID^E, Lamarck. 



Animal marine, the foot much reduced and devoid of a byssus. 

 Heart generally on the ventral side of the rectum. The gills fused to 

 the mantle. Monomyarian, the anterior adductor absent, but di- 

 myarian when young. 



Shell more or less distorted by early adherence to other objects, 

 fixed by the left and larger valve ; beaks subcentral or curved ; an 

 internal ligament in a triangular resihfer ; hinge area without teeth ; 

 the adductor-scar subcentral or posterior ; pallial hue indistinct ; 

 with a subnacreous or porcellanous inner and prismatic outer layer. 



Genus 1. OSTREA, Linne, 1758. 

 Ostrea, L., Syst. Nat., ed. 10, 1758, 696. Type : 0. edulis. L. 



Animal shaped like the shell, its mantle freely open and without 

 siphons, the edges double, and each bordered by short tentacular 

 fringes ; no conspicuous ocelli ; branchial leaflets not doubled on 

 themselves ; labial appendages triangular, connected around the 

 mouth by a plain membrane ; foot obsolete ; sexes distinct or united. 



Shell irregular in shape, attached by the left valve, which is the 

 larger and the more convex ; right valve usually flat or concave, 

 often smooth, and minus the radiating ridges which are usually so 

 conspicuous on the other valve ; lines or corrugations of growth 

 prominent on both valves ; ligamental area triangular or elongate, 

 symmetrical ; structure laminated, subnacreous ; muscle-scars large, 

 well pronounced, subcentral. 



Distribution. About 100 species are known from warm and tempe- 

 rate seas ; the genus does not occur in cold seas. 



Fossil in the Secondary and Tertiary, the majority in the Cretaceous. 



Remarks. The value and importance of the oysters as an article 

 of food is well known to everybody, and the oysters of Venice, Eng- 

 land, and the Dardanelles were much appreciated by the luxurious 

 Greeks and Romans of an ancient date. Useful information may be 

 found in : Philpot, " Oysters and all about them " (2 vols.) ; T. H. 

 Huxley, " Oysters and the Oyster Question " (English Illustr. Mag.. 

 1883-84, pp. 47-55, 112-21), and " Scientific Memoirs " (iv, 1902, 

 pp. 572-605) ; Saville Kent, " Oysters at the Antipodes " (Nature, 

 vol. xlv, pp. 43-45) ; M. F. Woodward, " Anatomy of the Larva of 

 Ostrea edulis " (P. Mai. S., i, 297). 



