401 



ribbing corresponds with the South Australian shell in the 

 width of the ribs, but they are almost straight, nearer together, 

 the bridging greatly thickened and proportionately shorter. 



The transverse ridges in the two lateral ribs are present 

 as mere nodules, irregularly spaced and not as sharp strongly 

 elevated ridges a6 in the two proceeding . This form easily 

 takes its place as a subspecies of Reeves' Callistochiton 

 antiquus. 



Callistochiton antiquus mayi, n. sp. 

 PL xlii., figs. 8 and 9. 



The only opportunity I have had of collecting Chitons 

 in North-western Tasmania was limited to one afternoon on 

 October 11, 1916, when I had an hour or so on the rocks at 

 a place called Penguin. Amongst the shells then collected 

 was a small Callistochiton quite new to me, which I concluded 

 and put aside as being Iredale and May's new Callistochiton 

 C. maivlei, which I had not then seen. Since then my friend 

 Mr. May has given me a specimen of that shell, and I find 

 that the Penguin shell is quite distinct, I sent it over to Mr. 

 May for his opinion, and he concurs with my view. I propose 

 naming if after Mr. May as an acknowledgement of the help 

 he has been in the elucidation of Tasmanian Chiton fauna. 



Description of differences. — This species differs from any 

 of the preceeding in the entire absence of longitudinal ribbing. 

 The whole pleural area is reduced to a network of which the 

 strands are so thick that the holes between are nearly filled in, 

 in the dorsal area this is absolutely the case, nothing but fine 

 granulose sculpture remaining. 



Under a pocket lens the pleural and dorsal areas appear 

 simply granulose, the network origin of the sculpture is quite 

 lost. Under a higher power, however, the network sculpture 

 survives in the form of numerous pits scattered towards the 

 anterior margin. 



The transverse ridges in the lateral ribs are almost as 

 defined as in the South Australian shell, but these ridges are 

 more numerous and closer together. Measurement, 8 mm. 

 x 5 mm. I consider this species diverges most from the dom- 

 inant form of all the subspecies here dealt with. 



Remarks. — In the absence of the examination of the Vic- 

 torian Callistochiton fauna, our knowledge of the effect or 

 otherwise of the Bassian Isthmus (Hedley : Proc. Linn. Soc. 

 N.S. Wales, xxvii., 1904) on the distribution of this genus 

 is very incomplete. In some respects the South-eastern Tas- 

 manian shell shows affinities with the Sydney shell ; but the 

 North-western Tasmanian shell is certainly more closely allied 

 to the South Australian than either of the other two. This 

 is certainly suggestive but inconclusive, until more Victorian 

 material is examined. I hardly think any additional word is 



