Older Tei'tlaiy of Victoria. 101 



of the latter is of tlie most meagre order, ami but for possessing 

 well authenticated examples of the species, it would be difficult 

 to be certain on many points, but by actual comparison the 

 following points )nay be noted : — C. dimorphophylla is more 

 regularly tumid and not depressed as in the ])resent new species, 

 and shows a marked posterior truncation, and a shorter anterior 

 end, the umbos being much further forward, and the radial 

 ribbing is of a much closer and finer character. 



This type of shell is also represented amongst living Australian 

 juollusca., and the species that appears most closely related is 

 C laqueata, Sowerby, which can be obtained living from the 

 Paramatta River, New South Wales, right up along the Queens- 

 land coast. This living species is, however, a strongly infiated 

 ;itid rather coarsely ornate form, as compared with our fossil 

 species. 



Chione cognata, sp. nov. (PI. XII., Fig. 5). 



Description. — Shell large, thick, and solid, broad I3' ovate, 

 regularly convex but not strikingly tumid, with a shallow but 

 broad lunule, and not deeply concave anterior to the umbo. 



Umbo broad and strong, incurved anteriorly, and situated 

 al)Out one-fourth the length of the shell from the anterior margin. 

 Anterior margin for the length of the lunule straight, thence to 

 and along the ventral margin regularly convex to the posterior, 

 where the shell shows an evident truncation from the post-dorsal 

 region, dorsal margin gently arched to the posterior truncation. 

 The ligamental groove is deep and very long, being about one- 

 half the length of the shell, and is margined by a broad, but 

 concave dorsal area which only shows lines of growth. 



The surface of the valves is crowded with very close and fine 

 radial riblets, which are broader than tlie interspaces, the riblets 

 thicken somewhat towards the ventral margin but still remain 

 broader than the interspaces ; the radial sculpture is crossed by 

 very fine lines of growth, and by strong regular concentric frills, 

 the frills at first are thin and delicate and usually the bases only 

 are pre.served, but towards the ventral margin they become very 

 thick and strong I'idges medially, tapering to thinner crenulated 

 frills towards the anterior and posterior of the shell, the 

 concentric frills taking up the character of the radial sculpture 



