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Definitions of Two New Species of South 

 Australian Polyplacophora. 



By Edwin Ashby. 



[Read September 3, 1900.] 



The discovery of the two new species of mollusca described in 

 this paper is one of the many valuable results of Dr. Verco's 

 dredging trips. Their discovery is of particular interest, because 

 both genera are, as far as our present knowledge goes, very 

 poorly represented in any part of the globe. Only one species of 

 Callochiton has before been recorded from this colony. Henry 

 A. Pilsbry, in his " Manual of Conchology," says of this genus 

 and its allied genera — " Of the whole series there are very few 

 species known. All of them are rare." And the other sub- 

 genus Stenochiton is only represented by two or three species, 

 though the allied subgenus Sten'oplax, to which the species herein 

 described bears some affinity, is a little better represented ; but 

 no representative has yet been recorded from this colony, 



Isehnochiton (Stenc chiton) pallens, sp. nov. Pi. i., figs, la— g. 



General Appearance. — Shell glossy, elongated, anterior portion 

 tapering to rear. Evenly arched and rounded, side slope curved. 

 Colour. — Cream, mottled with pink and pale brown. 



Anterior Valve. — Smooth and glossy, except for several growth 

 lines — that nearer the outer margin being the deeper. This 

 valve is longitudinally much shorter than is the case in 

 Stenochiton juloides and S. Pilsbry anus. Slits 13, at very irregular 

 distances apart. 



Posterior Valve. — Shield - shape tapering rapidly, mucro 

 posterior, only slightly raised. A deep sulcus traverses the whole 

 valve a short distance from the margin, preserving the shield 

 outline of the shell. A shallow diagonal depression crosses the 

 valve from the mucro to the suture. Surface of shell glossy and 

 smooth, slight growth lines visible under the microscope. Slits 

 six ; the teeth are very irregular in contour. 



Median Valves. — Uniformly smooth and glossy, showing 

 numerous growth lines, which are continued right across the 

 dorsal area. The three areas are hardly distinguishable, except 

 that the lateral area is slightly raised. The posterior margin is 

 finely serrated like a file where the valves are not worn. Four 

 of the median valves have one broad wedged-shaped slit on each 

 side ; two valves have two slits on each side. Inside of shell 



