70 



only in habits but also in food they are very distinct from any 

 other of our Australian forms of the Polyplacophora, together 

 with the external characteristics that differentiate them from 

 other genera of the Ischnochitonidae, suggests that further 

 investigation will reveal other differences, possibly internal 

 ones, and warrants the elevation of the subgenus Stenochiton 

 to the rank of a genus. I therefore propose to revive Adams 

 and Angas' genus Stenochiton, of which Stenochiton juloides, 

 Ad. and Ang., is the type. In some respects it is unfortunate 

 that this species should have to stand as the type of the genus, 

 because it exhibits several peculiarities that are not common to 

 those I consider its congeners. For the present we must deem 

 these specific distinctions only. The discovery of three or four 

 new species that show several striking characteristics in 

 common with Stenochiton juloides, that differentiate them 

 from other members of the Ischnochitonidae, makes it desirable 

 to retain only a portion of the characteristics cited by Adams 

 and Angas as distinguishing the genus and the adding of others. 



Generic description. — Shell usually elongated, highly 

 polished, almost unsculptured, convex, i.e., rounded or arched 

 as distinct from, carinated, plates of insertion small, multi- 

 fissate in the end valves, girdle clothed with very minute, 

 polished, imbricating scales. Living on plants of the order 

 Fluviales. Stenochiton (sensu strictoj will then be a subgenus 

 of the genus Stenochiton, distinguished by the elongated 

 character of the shell. A second subgenus will have to be 

 formed to receive a broad-shelled species that was collected by 

 the late Professor Tate on plants belonging to the order 

 Fluviales. This specimen has been placed in my hands by Dr. 

 Torr to be dealt with in a future paper. 



Conclusion. — I am hopeful that the investigations of 

 future workers, not only in the other States of Australia, but 

 also throughout the world, wherever plants belonging to the 

 order Fluviales are found, will, now we know where and how 

 to search, reveal many new forms of this genus. As Posidonia 

 oceanica, an allied form to the Australian member, occurs 

 extensively in the Mediterranean Sea and the European shores 

 of the Atlantic, it seems only reasonable to conclude that there 

 will be forms of Polyplacophora living on it that will exhibit 

 some of the modifications peculiar to the Stenochitons of 

 Australia. 



Stenochiton cymodocealis, n. sp. 



Pis. xiii. and xiv., figs. 1, 4, o, 11, and 12 (a, h, c, (/, e). 



General appearance. — Shell long, sides almost straight for 

 | of lateral, and then curving rapidly over dorsal area, width 

 of shell less than J of total length, dorsal area rounded, shell 

 exceptionally highly arched ; the whole shell is very polished. 



