265 



species is easily distinguished by its eroct girdle scales. Nearly 

 all the larger specimens were considerably eroded. 



Flaxiphora alhida, Blainville, and P. costata, Blainville. 

 These two species were living together at Lunawanna on the 

 sides and upper sides of large rocks at low water. While all 

 were covered with growth, many of them were in a state of 

 good preservation. Tlie vermiform marking or ribbing of 

 the former is in some specimens barely traceable, suggesting 

 a possible transition from one species to the other, but to 

 decide this point w^ll need a more extensive investigation than 

 the extent of this paper or the time available permits. Mr. 

 W. L. May writes me, "My experience is that, generally, 

 alhida is found in more sheltered situations. I have fre- 

 quently seen costata of large size on the outside rocks, exposed 

 to the full force of very heavy surf, as at Eagle Hawk Neck, 

 alhida being quite absent. At the same time, from shell 

 characters only, it is difficult to keep them separate." 



Kopionella, Ashby. A nice series was met Avith, but will 

 be dealt with further on in this paper. 



Acanthochiton sueri, Blainville, was very common at a 

 shallow depth ; a few were large with extremely wide girdles. 



Acanthochiton hednalli, Pilsbry. A few specimens were 

 taken in rather deeper water than the former species. 



Acanthochiton (yotoplaxj costatus, Ad. and Ang. One 

 very fine specimen was collected close to Lunawanna Jetty; 

 the girdle was of great width when alive, but shrinks much 

 in drying. The dry shell measures 24 x 14 mm. 



It will be seen that I have placed this species under the 

 sub7genus Notoplax instead of Macandrellus, Dall., he having 

 adopted Carpenter's name Macandrellus for di.M Acanthochiton 

 having no spicules on the girdle, citing A . costatus as type of 

 said genus. As well-preserved costatus from the type locality 

 have small spicules distributed over the girdle, I can see no 

 justification for separating them from the genus Notoplax. 

 Dr. Torr's species, from South Australia, is only differenti- 

 ated from A. costatus by the girdle being clothed densely 

 with coarse spicules, and therefore A. ruhrostratus, Torr, 

 must be considered a sub-species of costatus. The Tasmanian 

 form under review is freely covered with very small spicules 

 of the same character as the Sydney specimens, but more 

 numerous. 



Rhyssoplax oruktos, Maughan, although evidently rare, 

 several were secured at lowest tide, or nearly so. One inter- 

 esting feature, before unrecorded, is that in the juvenile form 

 the characteristic pitting is quite absent, so much so that they 

 might easily be mistaken for R. translncens, Hed. and Hull, 

 suggesting that both have the same ancestry. 



