63 



dredged by Mr. Gabriel in 5 fathoms, at Western Port, 

 Victoria, measuring 33x22 mm., in which the ray ribbing 

 of anterior valve is well denned, but the closely-packed inter- 

 mediate ribbing is hardly discernible, except near the margin ; 

 one of the coarse hairs on this specmen is 9 mm. long. Dr. 

 W. G. Torr kindly showed me his Victorian specimens, which 

 are similar to mine. 



Tasmanian form. — Both Mr. W. L. May (of Tasmania) 

 and Dr. Torr have been good enough to lend me their 

 Tasmanian shells for the purposes of this paper. Mr. May 

 writes that it is rare at Port Arthur. These Port Arthur 

 specimens show a considerable divergence from most of the 

 New South Wales shells, and are approached most nearly by 

 the dredged specimen, before referred to, from Western Port, 

 Victoria. The largest shell from Port Arthur is in Mr. May's 

 collection, and measures 41x31 mm., has practically no 

 decussation on dorsal or pleural area, but the smaller shell 

 shows it to some extent; the riblets on the anterior valve are 

 not as strong and the tail valve is more elevated than the 

 New South Wales type. But the small shell from Sydney, 

 before referred to, diverges from the type quite as much in 

 these respects. I therefore do not feel justified in separating 

 the Tasmanian Port Arthur shell from the New South Wales 

 and Victorian ones ; they all show the coarse, branching hairs 

 on the 'girdle, without the strange "spear-head" processes that 

 are present in the South Australian species. 



Re?narks. — The sculpture in this species shows a good deal 

 of variation. Speaking generally, the ribbing is coarser and 

 more defined in the northern shells and less conspicuous in the 

 Tasmanian. But these characteristics are hardly sufficiently 

 persistent to justify the making of a subspecies. It is just 

 possible that there may be two shells in New South Wales, in 

 which case one might be justified in separating the Tasmanian 

 form. If there are no intermediates the small shell I have 

 referred to might well be a second New South Wales species. 



In conclusio7i. — In none of these specimens from New 

 South Wales, Victoria, and Tasmania are the flattened finger- 

 like processes margining the girdle developed beyond the 

 incipient stage, and it is quite possible that this character may 

 be peculiar to the adult shells of the South Australian species, 

 but without the examination of a much larger amount of 

 material from the other States I hesitate to quote this 

 character as one of the distinguishing ones of the South 

 Australian shell. 



The measurements given in this paper show that the 

 adult South Australian shell is much larger, often double the 

 size, of its congener. 



