62 



A Review of the Australian Representatives 

 of the Genus Ischnoradsia. 



By Edwin Ashby. 

 [Read April 11, 1918.] 



This genus, one of the subdivisions of the Ischnochitonidae,. 

 Dall, was made by Shuttleworth in 1853 (Berner Mittheil,. 

 1853, p. 65), the characteristics being described as follows: — 

 "Valves having sharp but rather thick insertion plates, those 

 of the median valves with two or several slits. Girdle covered 

 with convex, pebble-like, smooth scales. Type, Chiton australis, 

 Sowerby." In addition to the Australian representatives, 

 several species have been found in Japanese waters. Four 

 species have been described as from Australia. 



In the "Mag. Nat. Hist. (Charlesworth)", vol. iv., June, 

 1840, Sowerby described (p. 290) Chiton australis (Conch. 

 Illus., fig. 46), Australia, and (p. 291) Chiton evanidus (Conch. 

 Illus., fig. 139), New Holland. Reeve in 1847, pi. xxi., 

 sp. 142, Chiton novae-hollandiae, New Holland, Mus. Brit., 

 and Chiton metallicus, Rve., Conch. Icon., t. 17, f. 1041, 1847. 



Pilsbry made I. evanidus and 7. metallicus synonymous 

 with I. australis, Sby., retaining two* Australian species only, 

 I. australis, Sby., and 7. novae-hollandiae, Rve. Iredale and 

 May, in the Proc. Mai. Soc, vol. xii., pts. ii. and iii., 1916, 

 revive the name evanida, Sby., and distinguish two species in 

 Tasmania, the Eastern corresponding with Sowerby's descrip- 

 tion of his evanidus :-— "Central areas smooth in the middle, 

 faintly striated at the sides; lateral areas rather elevated, with 

 radiating granular striae." And go on to say: — "The North- 

 west Tasmanian form differs in the absolutely smoothness of 

 its pleural areas, and seems identical with the South Aus- 

 tralian shells known as 7. novae-hollandiae, Reeve." 



I can endorse Iredale and May's contention that the 

 North-west Tasmanian form is identical with the South 

 Australian shell. The examination of a fairly extensive series 

 from North-west, Eastern, and Southern Tasmania, Mid- 

 Victoria, and South Australia in my own collection, and also 

 a series from Port Arthur, South-east Tasmania, from the 

 collections of Mr. W. L. May and Dr. Torr, establishes the 

 fact to my mind that only one species is common to these 

 localities. All the adult shells from the widely-extended places 

 are more or less ornamented with striae. "The absolute 

 smoothness of the pleural area," quoted by Iredale and May, 

 is only met with in juvenile shells, and the majority of adults 

 conform to Sowerby's description of evanida. 



