73 



Colour and markings. — General colour olive-green ; 

 pleural area white; dorsal area largely white, suggestive of a 

 white streak down the full length of the back. Lateral areas 

 olive-green, with two dark spots on the posterior margins on 

 either side, and a darker olive-green blotch near the apex. 

 All the areas are ornamented more or less with brown or dark 

 olive-green colour streaks. Under compound microscope the 

 megalopores are very pronounced on the anterior and posterior 

 valves and lateral areas of median valves, the surface being 

 apparently peppered all over with white spots. The pleural 

 and dorsal areas under the same power are decorated with a 

 number of white confluent streaks, which in the dorsal area 

 form a complete network or mesh. Inside of shell, pale olive- 

 green and white. 



Anterior valve. — Very distinct from others of this genus, 

 in that this valve is distinctly concave, broad, and flat, nearly 

 as long as wide, without sculpture. Under microscope (2-inch 

 objective and eye-piece) this valve is covered with white dots. 

 Icside of valve has 18 slits at fairly regular intervals, each 

 slit continued as a groove, irregularly and deeply pitted, to 

 the apex of the shell. The teeth are sharp, square edged ; 

 colour, pale olive-green and white. 



Posterior valve. — Longer than wide, mucro anterior, 

 hardly distinguishable, but in large shell from Cape Jervis 

 the mucro is practically median ; posterior slope very flat, 

 almost straight, but slightly concave. This feature is nothing 

 like so noticeable as in the anterior valve. Slits 19, each 

 continued in a groove to mucro ; margin of teeth between slits 

 slightly crenulate under 2 -inch objective. 



Median valves. — Uniformly smooth and glossy. The 

 lateral area is raised, but not as strongly so as in S. c/ymodo- 

 cealis. Slits 2 (in one case a suggestion of a third) ; the slits 

 are continued in grooves deeply pitted for their whole length. 

 The dorsal area is not beaked in some valves, but in others 

 slight beaking is perceptible. 



Note. — In a large specimen 20 mm. long, breadth just 

 under 5 mm. collected by myself at Cape Jervis, the lateral 

 area is distinctly raised, the line of demarcation between it and 

 the pleural area being clearly defined from the dorsal area to 

 the girdle. Two or three strong concentric sulci, following the 

 growth lines in the lateral areas, are present, giving a slightly 

 corrugated appearance to that area. Similar shells to these 

 large Cape Jervis ones were obtained by Dr. Torr at Corny 

 Point, Yorke Peninsula. Pleural and dorsal areas smooth, 

 highly polished. Under 2 -inch objective and eye-piece both 

 these areas are apparently thickly grooved with shallow wavy 



