934 MR. G. F. ANGAS ON AUSTRALIAN MOLLTJSCA. [NoV. 28, 



Jackson Heads. Length 2 inches 4 lines. The interior of the lower 

 valve is of a peculiar horny green colour. 



Fam. OsTREiD^. 



133. OSTREA PURPUREA. 



Ostrea eclulis, var. purpurea, Ilanley, Couch. INIiscel. pt. 3. 



This is the common "Mud-oyster," which supplies the Sydney 

 markets. Mr. Hanley regards it as a variety of Ostrea edulis, Linn., 

 a species that varies extremely according to its station in salt or 

 hrackish waters. On careful comparison of the Port Jackson shells 

 (especially the young) with those of Europe, I am of opinion that 

 the former may be separated as a distinct species under the uame 

 purpurea. The laminate scales are much larger, more regularly 

 frilled, and the valves are dentate at the margins ; the purple 

 colouring prevails more or less throughout, and in the young shells 

 exhibits a radiate style of painting. It occurs in various parts of 

 Port Jackson and the other harbours of New South Wales. My 

 largest specimen is from Johnson's Bay, and measures 6 inches 

 across. 



134. Ostrea mordax. 



Ostrea mordax, Gould, Proc. Boston Nat. Hist. Soc. iii. p. 346 ; 

 United States Exploring Expedition (Mollusca), pi. 43. f. o/.*) a, b. 



The "Rock-oyster" of the colonists. "The horizontal digita- 

 tions of the upper valve fitting into the erect canine teeth of the 

 lower valve, together with the denticles within, and the black elevated 

 cicatrice, may serve to identify this species." — Gould. The interior 

 is white, stained with blackish purple towards the margins. It is 

 excellent eating and of a delicious flavour. Common everywhere, 

 attached to rocks between tide-marks. Length 2 inches ; breadth 

 1 inch 7 hues. 



135. Ostrea circumsuta. 



Ostrea circumsuta, Gould, Proc. Bost. Nat. Hist. Soc. iii. p. 346 ; 

 United States Exploring Expedition, pi. 43. f. 576 a, b. 



This is a species of rare occurrence ; it is of a narrow elongated 

 form, denticulated and tinged with violet around the margin. The 

 interior is pearly white, with the scar of the adductor muscle violet. 

 Botany Bay. Length 2 inches ; breadth 1 inch. 



136. *Ostrea virescens. 



Ostrea virescens, Angas, anted., p. 911, PI. xliv. f. 13. 



A handsome species, very orbicular, frilled round the margins, 

 with the cardinal area large, flat, and triangular, and the interior of 

 a peculiar green hue. Attached to rocks and madrepores at low 

 tides in Watson's Bay. Length \h inch. 



