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A NEW RHYSSOPLAX. 

 By A. F. Basset Hull. 



When seeking material for a coloured plate of the different species of 

 Rhyssoplax {Chiton), 1 experienced some difficulty in obtaining a specimen of 

 R. bednalli Pilsbry, which is, perhaps, the rarest of the genus. The type shell 

 is, I understand, in England. Dr. W. G. Torr, of Brighton, South Australia, 

 kindly lent me one fine specimen, but learning that there was a better one in 

 the Adelaide Museum, I applied to the Trustees for permission to examine it. 

 On receipt of this shell I was surprised to find that it differed in such a degree 

 from Dr. Ton's specimen as to constitute a distinct species. I then applied 

 to the Trustees for permission to figure and describe the new shell, which was 

 readily granted. The description and figures were forwarded to the Trustees 

 for a decision as to publication, but were returned to me with an intimation 

 that Messrs. Ashby, W. L. May and Dr. Torr, were of opinion that the 

 shell was conspecific with Rliyssoplax bednalli Pilsbry. 



I nevertheless publish the description, being of opinion that the shell shows 

 sufficient variation from Pilsbry's shell to entitle it to recognition. 



RHYSSOPLAX SURRECTA, n. sp. Plate XXIVB., Figs. 1-8. 



Shell very long, narrow and elevated, carinated. Ground colour white, 

 flecked with pale reddish-brown on the lateral areas and beaks of median valves; 

 central areas washed with pale green, flecks of the same colour appearing on 

 the jugal tract. 



Anterior valve having twenty-six rows of more or less diamond-shaped pits, 

 increasing in size and sometimes bifurcating towards the margin, the surface 

 thus having the appearance of radiating riblets intersected by concentric lirae. 

 The apex of the valve is thrown slightly forward. Valve half as long as the 

 posterior valve. 



Median valves beaked, lateral areas deeply furrowed, the furrow containing 

 indications of additional grooves, in some cases one, and in others (notably valve 

 ii) two, the number of additional grooves not corresponding on the opposite 

 lateral areas of the same valves. The raised edges of the furrows are deeply 

 corrugated, imparting a serrated appearance to the posterior margins of the 

 valves. Central areas with eight to ten high ribs extending across the area, ex- 

 cept as regards the two nearest the jugum, the ribs almost as wide as the inter- 

 stices separating them. 



Posterior valve with sculpture of radiating rows of pits, similar to those 

 on the anterior valve, twenty-nine being indicated on the margin of the posterior 

 area: eight ribs in the anterior area. Muero very prominent, behind the centre. 



Girdle scales large, irregularly oval, striated, not highly polished. 



