75 



Stenochiton pallens, Ashby 



(Trans. Roy. Soc. S. Austr., vol. xxiv, p. 86, 1900). 

 PI. xiv., fig. 14 (a, b). 



General appearance. — Shell glossy, elongated, 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 very short, being twice as wide as 

 long (see measurements). Slits 13, at very irregular distances 

 apart. 



Posterior valve. — Shield-shape, tapering rapidly; mucro 

 posterior, only slightly raised. A deep sulcus traverses the 

 valve a short distance from the margin, preserving the shield- 

 like 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; this sculpture is very shallow. Four of the median 

 valves have one broad wedge-shaped slit on each side; two 

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

 white, sinus broad and shallow, sutural laminae only slightly 

 produced. 



Girdle. — Under pocket lens appears whitish and felt- 

 like. The margin fringed with white spicules, but under 1- 

 inch objective the girdle is seen to be crowded with masses 

 of small, irregular, imbricating scales, which are finely 

 striated. Owing to the condition of girdle I have been 

 unable to determine the exact shape of scales or verify the 

 statement that they are finely striated. In the foregoing I 

 have where possible followed the original description. 



Measurements. — Anterior valve of disarticulated type, 

 longitudinal length 1*75 mm., breadth 3'5 mm. Anterior 

 valve of co-type, longitudinal length 2'5 mm., breadth 5'5 

 mm. Posterior valve about the same width at anterior 

 margin as valve is long. Width 5 mm., tapering evenly to 

 "2 mm., then rounded off abruptly. Length of valve, 4*5 mm. 

 Valves 2 to 6 are all 6 mm. wide and about 3 mm. in length 

 at the dorsal area, and are therefore twice as broad as long. 

 Valve 7 tapers a little. 



Habitat. — I think the statement in the original descrip- 

 tion, Gulf St. Vincent, is probably correct, but one of the 



