123 



■fff Australian. 



9. Placunanomia zealandica. /yht 



Suborbicular, white, smooth ; upper valve with distant radiating 

 grooves ; internally dark green. 



Upper valve with two confluent scars ; upper oblong, longitudinal, 

 lower rather small and more transverse. 



Anomia Zealandica, Gray, in DieffenhacK s New Zealand, ii. 261, 

 1843. 



Hab. New Zealand; on the inside of mussel shells. 



10. Placunanomia ione. 



Shell white, laminar ; edge of the laminse with small, slender, elon- £} JL 

 gated processes ; internally green. 



Lower muscular scars small, round, on the lower hinder edge of 

 the larger one • sinus or perforations large. 

 . — Hab. Australia, Sydney ; on rocks, Mr. Strange. 



Mus. Cuming ; three specimens. ? Van Diemen's Land. ^"^ 



ff/yh ~- Dr. Sinclair, Brit. Mus., a single dorsal valve. 



11. Placunanomia colon. 



Shell (upper valve) flat, with rather irregular, flat, radiating ribs ; 

 white, lower spotted ; upper valve with two separate scars ; the upper 

 one oblong, longitudinal, the lower much smaller, circular. 



Hab. ? 



Mr. Cuming's Collection (no. 10). Mr. Humphrey's Collection; 

 a single upper valve of a rather yomig shell. 



Here may be added the description of a new genus, intermediate 

 between this family and Placunidce. 



in. Hemiplacuna. 



Shell free ; valves orbicular, flat, external surface minutely laminar 

 and radiately striated, especially on the edge of the plates ; muscular 

 scar in each valve single, nearly central, circular ; the right valve flat, 

 with a large oblong, elevated transverse process for the cartilage, 

 having a very small concavity in the inner surface in front of the car- 

 tilaged process representing the sinus in Anomia ; the left valve rather 

 more convex, with an oblong transverse pit for the internal cartilage 

 under the umbo. 



Hemiplacuna, G. B. Sowerby, MSS. 



This shell has all the external characters of the flat species of Pla- 

 cuna, and has the same muscular impression ; but instead of having 

 the two linear diverging ridges and grooves to give attachment to the 

 cardinal cartilage, it has an oblong elevated process in the right valve, 

 and an oblong cavity in the left, exactly similar to those found in the 

 genus Anomia ; and on the inner surface of the right valve, just in 

 front of the base of the process which supports the cartilages, there 

 is a small shallow roundish pit with a short furrow towards the centre 

 of the shell, which is evidently a rudimentary representation of the 

 sinus found in the genus Anomia. This sinus is not visible on the 

 outer surface of the shell. 



