264 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Stenochiton cymodocealis, Ashby, 1918. 



(Trans. Roy. Soc. of S. Austr., vol. xlii, 1918, pp. 70-2, pis. xii and 

 xiv, figs. 1, 4, 5, 11, and 12, a-e, Ashby), (Journ. and Proc, 

 Roy. Soc. of W. Aiistr., vol. vi, pt. 2, 1919-20, Ashby). 



This strange little, highly polished Stenochiton lives on the 

 cylindrical stenas and not on the flat leaves of Cymodocea. For this 

 reason it is impossible to flatten out the girdle after death, but by 

 placing the living specimens in a glass tube of sea water some of them 

 will affix themselves to the glass, and if then the water is poured 

 off and the Chitons rapidly dried they will dry flat. If allowed to die 

 in the water, which they do quickly, they will relax, fall from the 

 glass, and contract. This little species is often decorated with 

 blotches of pink and white, thereby imitating the colour of the 

 calcareous growths more or less present on the stems of Cymodocea. 



To find this Chiton the plants of Cymodocea want pulling up as 

 low down as possible, the specimens usually being found only a 

 few inches above the sand. As before stated, since one was aware 

 oi the habits of this species one has found it present in every place 

 where Cymodocea has been met with, in South Australia, and, in 

 November, 1920, as far north as Geraldton in Western Australia. 



Dr. W. Gr. Torr and myself for twenty years had worked over 

 stones buried in beds of Cymodocea without discovering this species, 

 whereas one had only to spend a few minutes in examining the stems 

 of the sea-grass through which we were wading to have found a 

 number of specimens. 



Stenochiton posidonialis, Ashby, 1918. 



(Trans. Roy. Soc. of S. Austr., vol. xlii, 1918, pp. 72-4, pis. xiii 

 and xiv, figs. 2, 6, and 13, a-d, Ashby), (Journ. and Proc. 

 Roy. Soc. of W. Austr., vol. vi, pt. 2, 1919-20, Ashby). 



In this species both the anterior and posterior valves are very 

 long, and the former is distinctly concave and the latter slightly so. 

 In colour and markings it is extremely variable ; the general colour 

 is green or greenish-brown, but I have taken specimens that are 

 bright orange, others with a dark -brown dorsal line, and again 

 magpie-marked, blotched with dark brown with a pale ground 

 colour. 



In some localities they rarely exceed 10 mm. in length, whereas 

 in others they are more than double, and often of a very brownish 

 colour. This species also occurs freely in Western Australia, where 

 the magpie or blotched variety is more numerous than in this State. 



It lives usually just above the sand, on the ribbon-like leaves of 

 Posidonia ; it is necessary to pull up the host plant from very low 

 down or the Chiton may be left behind. 



