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NOTES ON THE GENUS STENOCHITON AND THE DISCOVERY 

 AND RECOGNITION OF THE TYPE OF BLAINVILLE'S 

 CHITON LONGIGYMBA IN STENOCHITON JULOIDES, ADAMS 

 AND ANGAS. 



By Edwin Ashby, P.L;S. 



Read 9th March, 1923. 



This remarkable genus of Polyplacophora, while evidently rightly^ 

 placed under the Isclinocliitonidae, in habits and characters its 

 members are evidently widely removed from any other known form. 



Instead of harbouring or living on stones, shells, or blocks of 

 timber, the members of this genus have as their host and probably 

 their food supply, various species of that order of marine flowering 

 plants known as Sea Grasses. 



The genus Stenochiton was formed by Adams and Angas in 1864, 

 for the reception of the South Australian shell described by them 

 under the name S.juloides (Proc. Zool. Soc, 1864, p. 193). As shown 

 later, the same shell had been described by De Blainville in 1825, 

 under the name of Chiton longicymha, from a specimen collected by 

 Peron and Lesueur, at King Island in 1803. 



The next species, S. pilshrymius, was described by Bednall in 

 1897 (Proc. Malac. Soc, vol. ii, pt. 4) as having been found " on 

 sea- weed ? Zostera ". This being the first intimation of the 

 possibility of its habitat being other than rocks, etc. In 1900 the 

 writer described a third species under the name of S. pallens, Ashby. 

 In May, 1918, he read a paper before the Royal Society of S. Australia 

 showing that Bednall's description did not apply to any particular 

 species, but that the figures and description were a sort of con- 

 glomerate made up from parts of two or more species. In the same 

 paper he described two more forms under the names of posidonialis, 

 Ashby, and cymodocealis, Ashby, and finally in a paper read before 

 the same Society in July, 1919, he described a further species as 

 pilshryanus, Bednall. 



It will be seen that we have five known species all described from 

 South Australia. 



Habitat. — The writer in his paper (Trans. Roy. Soc. of S. Austr., 

 vol. xlii, 1918) was able to show that all the members of this genus 

 Hve, not as had been previously supposed on " Pinna shells, old 

 boots, glass bottles ", or on rocks, but on the growing stems and 

 leaves of flowering plants known as " Sea Grasses ", being found 

 during the day time hidden away in the brown sheaths of old 

 Posidonia leaves, usually buried several inches deep in coarse shell 

 grit and sand. They probably come out at night time and feed on 

 the leaves of growing Posidonia, only returning as day approaches 

 to the protection of the sheaths near the roots of the plant. One 

 needs a digging tool to get the plant up by the roots, and then in 

 sheltered localities the Stenochiton is found to be quite common. 



