237 



A REVIEW OF THE AUSTRALIAN REPRESENTATIVES OF THE 

 GENUS CRYPTOPLAX, ORDER POLYPLACOPHORA. 



By Edwin Ashby, F.L.S., M.B.O.U. 



[Read August 9, 1923.] 



Plates XVI. to XIX. 



Family Cryptoplacidae, Dall. 

 Genus Crytoplax, Blainville, 1818. 



A group of vermiform chitons with greatly reduced valves, often widely 

 separated, and with usually a great width of girdle, which is densely covered 

 with spicules ; having three slits in the insertion plate of the anterior valve, but 

 no slits in any of the others. 



Introduction. — The brief resume of the Australian members of this genus 

 given on p. 578 in the writer's paper on the Types, in the Paris Museum, needs 

 revision, both on account of my notes on the examination of the types in the 

 British Museum not having been referred to in the preparation of that paper, 

 and also because of the recent discovery of Thiele's Cryptoplax michaelseni, at 

 Carnarvon, in Western Australia. This latter was, for reasons stated below, 

 somewhat imperfectly described, and has hitherto only been known from the 

 unique specimen in the Berlin Museum. One is now able to deal with the 

 group in a much more thorough manner. Descriptions are appended of the 

 two forms described by Dr. Thiele, as up till now no description of these has 

 been published in English. 



Cryptoplax striatus, Lamarck, 1819. 



PI. xix., fig. 5. 



(Chitoncllus striatus, Lamarck, An. S. Vert., vi., p. 317, 1819 ; Ashby, Trans. Roy. Soc. 

 S. Austr., vol. xlvi., p. 577.) 



The discovery of Lamarck's type of C. striatus in the Paris Museum, referred 

 to in my paper (I.e.), settled the long outstanding question as to which of our 

 known shells was C. striatus. The type came from Kangaroo Island, and the 

 shell is the common one in the State of South Australia, but is distinct from the 

 shell that has been known under the name of C. striatus from Sydney. It is 

 easily distinguished from the more northern species in that, in the adult shells, 

 the sculpture of C. striatus is always longitudinal, coarse, wavy ridges, and that, 

 in the adult, the valves, after the first four, are usually more or less spaced ; 

 the girdle is densely spiculose, the spicules being long and much curved. 

 Juvenile shells of this species are decorated with longitudinal rows of granules, 

 which are less bead-like than is the case with the Sydney shells ; this feature 

 can be observed near the umbo in the adult. I have collected this species as far 

 west as Venus Bay, and have specimens from Philip Island, and one adult 

 given me by Mr. Tom Iredale, from Port Fairy, near the New South Wales 

 border, in Victoria. 



Cryptoplax striatus. Lam., var. gunni. Reeve, 1847. 



(CliitoncUus gunni. Reeve, Conch. Icon., f. 5, 1847; non giinni, Rv. of Ashby, (I.e.), 

 auct.) 



I saw in the British Museum last year Reeve's type of this shell and noted 

 that it was conspecific with C. striatus, Lam., from Tasmania and South 



