34 I'llOCEKDINGS OF THE MALACOLOGICAL SOCIETY. 



Remarks. — In sculpture aiitl foim this shell is closely allied to 

 i'. rcelafa (Reeve), differing at sight in the girdle characters. 



Thiele (Revision, p. 23), meeting with Neozelanic Plaxiphora, has 

 indicated the differences between P. calata (Reeve) and a young 

 Plaxiphora from Lyttelton, New Zealand, and has also named the 

 Chatham Island species P. schauinslandi. When I discussed 

 Australasian PJaxiphora (Pmc. Malac. Soc, vol. ix, pp. 92-100, 

 1910) I had no Lyttelton specimens before me. I had largely 

 collected there, and receiving specimens I at once dissected some, and 

 found them to agree with Thiele's description. When I collected 

 them it was with much misgiving that I associated all my small 

 Plaxiphora together as P. cctlata (Reeve). That species, determined 

 by P. terminalis (Smith), was much larger, more elevated, differently 

 coloured, with different shape and different girdle characters, whilst 

 it lived lower down. Thiele's shell is the very common smaller shell 

 living near high-water marii and always much ei'oded. A new 

 7iame is not needed, as I would unhesitatingly identify the latter with 

 Tonicia %ig%ag, Huttou (Trans. N.Z. Inst., vol. iv, p. 181, 1872), and 

 it should be known as 



Plaxiphoka (Maoricuiton) zigzag (Hutton). 



The Kermadec species is allied to the true P. calata (Reeve) and not 

 to P. zigzag (Hutton). 



Family CRYPTOPLACID^. 



Thiele has amalgamated Pilsbry's two families Acanthochitidse and 

 Crypto pi acidae under the latter name, admitting two sub-families of 

 ])ractically the same dimensions and names. He also admits as 

 distinct genera Cryptoconchus and Acanthochites, a course I fully 

 endorse. I note this here, as a valve which would seem referable to 

 CryptoconcJuis was found by Mr. Roy Bell in a rock pool on the east 

 coast. Valves of two species of Acanfliochites were met with in 

 dredgings ; both were minute, but no complete specimen was procured. 



Family ISCHNOCHITONID^. 

 Genus Ischnochiton. 

 hchnochiton, Gray, Proc. Zool. Soc, 1847, pp. 127, 168. 



Type (by subsequent designation, Gray, 1847), Chiton textilis, Gray. 



Thiele subdivides this genus in a somewhat conservative manner, 

 recognizing three sub-genera, Ischnochiton, Stenoplax, and Chondro- 

 pleura. Under the first he places with sectional rank only 

 Ischnoradsia, Sfenochiton, and Ileterozona; the other divisions do not 

 interest Australasian students. None of these, however, should 

 admit Stenochiton as of sectional value only, whilst I should prefer 

 Ischnoradsia given at least sub-generic rank. As, however, the 

 Kermadec species is referable to Ischnochiton, s.str., I will defer 

 discussion of the Thielean classification until I deal with species of 

 Ischnoradsia at a later date. 



