136 Proceedings of the Royal Society of Victoria. 



the neighbourhood of the luuule is markedly concave to a little 

 beyond the lower end of the lunule, thence the anterior margin 

 is regularly convex and protruding well forward before joining 

 the convex ventral margin ; post-dorsally flat on the dorsal 

 surface, but the margin is slightly convexly rounded to meet the 

 ventral margin with which it forms a very obtuse angle. 



Externally the valves are ornamented with very numerous 

 close-set concenti'ic ridges, which are flat medially, but on account 

 of being set somewhat obliquely appear slightly acutely elevated 

 towards the umbo, becoming distinctly lamellose anteriorly and 

 posteriorly, the lamella? being directed towards the ventral mar- 

 gin and being most highly elevated along the posterior and 

 anterior slopes of the valve. The concentric ridges become 

 slightly broader towards the ventral margin, the intervening 

 gi'ooves are comparatively shallow and very much narrower than 

 the ridges, usually considerably less than one-half their width, 

 and becoming broader as the ridges become lamellose. The 

 number of concentric ridges in more than half a dozen specimens 

 of about the same dimensions as Dosinia johnstoni., Tate, namely, 

 29 mm. by 27 mm., average forty-nine in ten millimetres from 

 the ventral margin ; in specimens of larger dimensions they be- 

 come gradually less in number, and in the largest specimen yet 

 to hand, which measures 62 mm. by 57 mm., we have only 

 eighteen concentric ridges. 



Both ridges and grooves very flnely, regularly, and closely con- 

 centrically striate, the strise of the grooves becoming distinctly 

 lamellose ventrally and laterally, usually more distinct at the 

 posterior end. Internally the hinge is thick and strong in the 

 adult form, with a well-defined and deep ligaraental area post- 

 dorsally ; the hinge of the right valve bearing three strong 

 cardinal teeth, the middle one being slightly bifid, whilst the 

 posterior one is more distinctly so ; there are also two rudi- 

 mentary anterior lateral teeth at the base of the lunular area ; 

 the left valve also carries three strong cardinal teeth, the middle 

 one only being sliglitly Ijitid, and one strong anterior lateral 

 tooth. The pallial sinus is very Ijroad at the base and deeply 

 protruding into the shell liorizontally and vertically Ijeyond the 

 centre of the valve, apex usually convexly rounded, occasionally 

 acutely angular. 



