REPORT ON THE LAMELLIBRANCHIATA. 61 



This is a thinnish species, nearly equilateral, ovately trigonal, longer than liigli, some- 

 what acuminate at both ends, more especially posteriorly. It is rather glossy, very 

 finely striated by lines of growth, and sculptured on both sides beneath the dorsal line 

 with somewhat strong sulci, which become gradually coarser as the shell increases. The 

 general tone of the valves is light fawn, varied with numerous narrow olive-brown rays, 

 and purple tips to the umbones. The dorsal area has a lanceolate white space in front 

 of the beaks, and a narrower one behind them, which are bordered with a brownish colour. 

 The dorsal margin is very oblique and only slightly curved in front, but rather more 

 arched and about equally sloping behind. The lower outline is regularly and broadly 

 arcuate, forming anteriorly with the upper slope a rather sharply rounded extremity, the 

 opposite end being roundly angulated. The interior of the valves is livid purplish, paler 

 towards the margin, which is fawn coloured, and bluish-white beneath the umbones. 

 The hinge-plate and the teeth are white. The pallial sinus moderately deep, some- 

 what sharply rounded at the end, • and does not reach quite half-way across the 

 valves. 



Length 31 mm., height 21, diameter 12^. 



Habitat. — Brisbane water, Queensland, di-edged at a depth of 5 fathoms on a sandy 

 and shelly bottom by J. Macgillivray during the voyage of the " Eattlesnake ; " also 

 Port Jackson, New South Wales, in 4 to 18 fathoms (Challenger) ; Moreton Bay 

 (A. Adams). 



This is possibly the species referred by Angas ^ to Mactra luzonica of Deshayes, to 

 which it is very closely related. That species is, however, a somewhat thicker shell, a 

 trifle more elongate, having the hinder side rather longer than the anterior, whilst, in the 

 present species, the latter portion is slightly the larger. It is more strongly striated, 

 especially towards the anterior end, where the valves are distinctly concentrically 

 sulcate. It is also almost totally devoid of radiating markings, has no whitish mark 

 beneath the umbones in the interior, and has a smaller and shorter paUial sinus. It is 

 said to have been found at the Island of Luzon, and specimens were collected on the 

 coast of Arakan by W. T. Blanford, Esq., who liberally presented a set, together with a 

 very valuable collection of shells from that country, to the British Museum. 



The types in Cuming's collection found at Moreton Bay by Mr. Strange are young 

 shells, and of a paler tint than more adult specimens. The interior also lacks the livid 

 purplish colour so characteristic of the full-grown shell, and the beaks are paler than 

 usual. In aU other respects there is no difference, the form, sculj^ture, hinge and 

 pallial sinus corresponding exactly with the larger specimens from Port Jackson and 

 Brisbane. But little attention must be paid to the colours ascribed to this species 

 by its describer, for I was once informed by Mr. G. F. Angas that ^Ir. A. Adams was 

 colour-blind. 



1 J'roc. Zoul. Hoc. Lund., 1867, ]'. UlU. 



