158 



<?. strigosa, but is proportionately shorter, the'concentric ridges 

 are flat, and not at all undulose. 



Chione dictua, spec. nov. Plate xvi., fig. 2. 



Transversely-oblong, inequilateral, rather depressed, broadly 

 rounded in front, narrowed and obliquely truncate behind. 

 Umbo acute, incurved, directed forward, situated in the anterior 

 third ; dorsal margin about equally sloping on both sides, 

 straight behind, and feebly concave in front of the umbo. 

 Surface ornamented with flat closely-set riblets somewhat 

 irregular in thickness, but always wider than the linear inter- 

 spaces, and decussated by concentric striae and raised threads, 

 more distant from each other than are the radial riblets, the 

 concentric threads acquire the form of thin slightly elevated 

 lamellae at the two extremities. Lunule lanceolate, slightly 

 concave, and medially elevated, sculptured with fine lamellae of 

 growth and circumscribed by a deep groove. Margin of valves, 

 except post-dorsal, finely crenulated. 



Dimensions. — Antero-posterior, 10 ; umbo-ventral, 7 ; and 

 sectional diameter of both valves, 35 millimetres. 



Locality. — Oyster beds of the River Murray Cliffs at Nor'- 

 West Bend. 



C. dictua has some affinity to C. striatissima and to young 

 examples of C. gallinula, but the shape is different, and the 

 sculpture very much finer. 



Genus Cytheeea. 

 synopsis of species. 



A. Lamellate rugae on the posterior slope. 



Transversely-ovate, acuminated posteriorly. 



C. paucirugata. 

 More triangular, truncated behind. C. Murrayana. 



B. Smooth. 



Transversely-oval, somewhat produced and truncated 



behind. C. tenuis. 



Ovately-trigonal, rounded behind. C. eburnea. 



Oval, subacuminated posteriorly. C. submultistriata. 



Gytherea paucirugata, spec. nov. Plate xiv., fig. 14. 



Transversely-ovate ; somewhat acuminate at both ends, espe- 

 cially behind ; very inequilateral, moderately convex, thick ; 

 the front-dorsal slope is straightish, or a little incurved at the 

 lunule, and much more descending than the post- dorsal margin, 

 which is at first broadly curved, finally narrowly obliquely 

 truncated ; the ventral margin is widely arched, but is indis- 

 tinctly sinuated in front of the post-ventral angulation. 



The umbones are small, approximate, situated about one- 



