400 



Callistochiton antiquus meridionalis, n. sp. 

 PL xlii.j fig. 7. 



Introduction. — In setting out to describe a new form of 

 Callistochiton I collected on the North-west coast of Tasmania 

 I have been compelled to examine specimens from the type 

 locality, New South Wales, which was described under the 

 name C. antiquus (pi. xlii., fig. 6) by Reeve in 1847, and 

 compare them with the Tasmanian shells and South Aus- 

 tralian shells, with the result that I find that our South 

 Australian shell must receive a distinguishing name before 

 the new Tasmanian shell can be put in its right niche in 

 our classification. 



Description of differences. — In the South Australian shell 

 the longitudinal ribbing in the pleural area is broader, less 

 elevated, more wavy and granulose than in the shell from New 

 South Wales, also instead of running parallel to the midline 

 they are deflected somewhat towards it. The bridging of the 

 South Australian shell is only slightly lower than the ribs, 

 whereas in the northern shell the bridging is deep, not stand- 

 ing up nearly as high as the longitudinal ribs ; also the trans- 

 verse ridges on the two lateral ribs are less elevated, further 

 apart, and more numerous in the South Australian form. A 

 still more striking difference is revealed when the valves are 

 disarticulated. The anterior margin of the tegmentum is 

 almost straight in the Sydney shell, but in the South Aus- 

 tralian one it is produced forward almost to a point. The 

 sutural laminae are broad and straight-edged in the northern 

 shell, but are narrow and more produced forward in the South 

 Australian shell. Another marked feature is that while in 

 both the articulamentum is continued in front of the 

 tegmentum across the sinus, in the South Australian shell it 

 is divided into minute teeth — I counted 10 slits — the edge of 

 each of the minute teeth is curved, giving a scalloped margin 

 to this portion of the articulamentum, whereas in the Sydney 

 shell it is straight-edged, the slits being suggested by slight 

 grooves. I am suggesting the subspecific name of meridional is 

 for the South Australian shell. I have found this shell where- 

 ever I have collected in this State. 



Type is from Marino. I am presenting it to the South 

 Australian Museum. 



Callistochiton antiquus mawlei, Iredale and May. 



This species was described from Port Arthur, South-east- 

 ern Tasmania by Messrs. Iredale and May. It differs again 

 from either of the foregoing in that the longitudinal ribbing is 

 persistent right over the dorsal area, the irregular network 

 present in the two former being absent. The longitudinal 



