182 PROCEEDINGS OP THE MALACOLOCICAL SOCIETY. 



6. OsTREA ANGASi, Sowerby. 



Ostrea angasi, Sowerby, 1871, Concb. Icon., vol. xviii, pi. xiii, fig. 27 ; 



Suter, 1913, Man. N.Z. Moll, p. 888, pi. Ivii, fig. 3. 

 Ostrea reniformis (not Sowerby), Hutton, Jo urn. de Concbyl., 



vol. xxvi, p. 56 ; Hutton, 1880, Man. N.Z. Moll, p. 175. 

 Ostrea tatei (part), Suter, 1913, Man. N.Z. Moll, p. 889, pi Ivii, fig. 4 

 (tbe New Zealand sbell only). 



Tbe cbaracters of tbis species, so far as it is distinguisbed from 

 otber New Zealand species of Ostrea, are tbe irregular low distant 

 radiating ribs and coarse laminations on tbe left valve, and tbe fine 

 brown brittle laminae on tbe rigbt or flat valve. On muddy bottoms, 

 wbere tbe sbell is free or only sligbtly attacbed, tbe left valve is 

 regularly convex. Wben a large portion of tbe left valve is attacbed 

 to a rock it always turns more or less sbarply up along tbe margin 

 of tbe area of attacbment. Tbis is a necessary adaptation for tbe 

 animal to get tbe space it requires between tbe two valves. It 

 seems curious tbat tbe convex valve is tbe one tbat is attacbed to 

 tbe rock and tbus made subject to special adjustment, a circum- 

 stance tbat migbt bave been avoided bad tbe flat valve been tbe 

 lower one. Tbe species reacbes its largest size in water of 15 to 

 20 fathoms in Foveaux Strait. Between tide-marks tbe sbells 

 are usually smaller, and being attacbed to rocks bave tbe free 

 portion of tbe lower valve turned at an angle to tbe attacbed portion. 

 Sbells only 2 or 3 cm. in diameter, at Spirits Bay on rocks between 

 tides, I refer to this species. 



Tbe rock form of tbis species from tbe southern portion of New 

 Zealand is classed by Suter with tbe Eocene fossil from Australia, 

 which he then names 0. tatei (Man. N.Z. Moll, p. 889, 1913). 



7. Ostrea corrugata, Hutton. 



Ostrea corrugata, Hutton, 1873, Cat. Tert. Moll. N.Z., p. 35 ; Suter, 



1913, Man. N.Z. Moll, p. 890, pi Ivii, fig. 5. 

 Ostrea reniformis (not Sowerby), Suter, 1913, Man. N.Z. Moll, 

 p. 892, pi Ivii, fig. 7. 



There is a small oyster found on inter-tidal rocks in harbours 

 and, in deeper waters, in Hauraki Gulf. I have examined specimens 

 from Auckland, Welbngton, Lyttelton, and Dunedin Harbours. 

 It also occurs in Pliocene beds near Wanganui. It usually has a thin 

 sbell, with many often high, close, radiating ribs, three or four ribs 

 to 1 cm., and is usually attached by only a small portion of tbe 

 left valve. It is easily separated from A. angasi by these characters. 

 The right valve often bears three broad, radiating, dark bands. 



Tbe type of Hutton' s species, a Pliocene fossil, is in the Dominion 

 Museum. Tbe sbell is more solid than recent forms and has larger, 

 higher, and more distant ribs ; otherwise it agrees. Suter figures 

 an oyster from Auckland Harbour under tbe name of 0. reniformis. 



