18/8.] MR. G. F. ANGAS ON NEW MARINE SHELLS. 863 



or with very fine concentric lines of growth, pale horn-colour, with 

 a single row of pale blue spots and crescent-shaped opaque markings 

 extending from the apex centrally, more or less along the outer arc 

 of the shell ; apex anterior, recurved, submarginal ; aperture nar- 

 rowly orate, margin simple, entire ; interior pearly white, shining. 



Diam. maj. 3, min. 1|, alt. 1 line. 



Hab. Holdfast Bay and Aldinga Bays; parasitic on seaweed. 



Mysella donaciformis, n. sp. (Plate LIV. fig. 13.) 



Shell quadrately cuneate, moderately solid, equivalve, very inequi- 

 lateral, subventricose, compressed towards the base, white, shining, 

 finely concentrically ridged ; dorsal margin slightly arcuate posteriorly, 

 short and abruptly descending anteriorly ; ventral margiu a little 

 convex ; umbones somewhat tumid ; beaks distinct, incurved, 

 approximate. 



Long. 3, alt. 2, lat. 1 line. 



Hab. Holdfast and Aldinga Bays, St. Vincent's Gulf. 



In the 'Proceedings' of this Society for 18/7, page 176, I 

 gave the diagnosis of the genus Mysella, for the reception of a 

 small bivalve from Port Jackson, which I described as Mysella 

 anomala. I have subsequently received from Professor Tate one or 

 two examples of the same species from South Australia, together 

 with a second form of the genus, of a more cuneate shape than the 



type, now described above as M donaciformis. 



* 



Lepton australis, n. sp. (Plate LIV. fig. 14.) 



Shell quadrately orbicular, compressed, equivalve, nearly equi- 

 lateral, thin, very slightly gaping at the sides, white, very finely 

 concentrically striated ; dorsal margin arched, ventral margin nearly 

 straight ; beaks small, produced and acute. 



Long. 4, alt. 3, lat. \ line. 



Hab. Glenelg, and Port Creek. 



Belonging to the typical form of the genus, with the surface of 

 the valves finely striated but not shagreened. 



Lucina (Codakia) tatei, n. sp. (Plate LIV. fig. 15.) 



Shell quadrately ovate, subventricose, moderately solid, subequi- 

 lateral, white, concentrically ridged, the ridges closer near the 

 umbones, and more distant towards the base, and crossed on both 

 sides with radiating ribs, that become slightly nodulous at the inter- 

 sections ; dorsal margin deeply excavated in front, nearly straight 

 and rapidly descending behind ; ventral margin arcuate, rounded in 

 front, forming an obtuse angle where it joins the dorsal excavation ; 

 umbones very acute, incurved and approximate. 



Long. 4, alt. 3, lat. 1| lines. 



Hab. East side of St. Vincent's Gulf, and Cape Northumberland. 



This little species is quite distinct from L. quadrata, Angas 

 (P. Z. S. 1877, p. 1/6), from Port Jackson, although of a somewhat 

 similar form. 



