68 



the pleural and lateral areas, also other olivaceous markings 

 are present. 



Anterior valve. — Unsculptured ; under a high power the 

 valve is seen to be covered with whitish spots, suggesting 

 regular decussation, but the brownish-olive mottling so gener- 

 ally covers the valve that in many parts the white spots are 

 indistinguishable. The shell is convex, evenly rounded and 

 arohed, about twice as broad as long, teeth well defined, with 

 rounded, slightly wavy edges, eaves well developed, teeth 

 propped or fluted, slits 16, inside whitish and glassy. 



Posterior valve. — Unusually broad for this valve, being 

 only slightly less broad than the median valves, mucro slightly 

 anterior, posterior slope evenly rounded but steep, convex. 

 The portion of shell anterior to mucro is distinguishable from 

 the posterior part, being smooth and slightly paler in colour; 

 growth lines are visible on the posterior portion, also a slight 

 ridge divides the portions, starting at the mucro and running 

 diagonally to the suture. Behind the mucro is another half- 

 moon-shaped shallow T ridge, making a sort of false mucro. 

 Inside the shell is white and transparent, multinssate. I 

 counted 9 clearly-defined slits with square, broad-ended apices 

 in the small terminal broken portion, but did not disarticulate 

 the other and larger part of this valve. The teeth are round- 

 edged, and are fluted or propped on the inside as in the 

 anterior valves, eaves distinct. 



Median valves. — Uniformly smooth, glossy, and unsculp- 

 tured ; the anterior margin of the lateral area is slightly raised, 

 in some of the valves, especially in valve 2. The dorsal area 

 barely distinguishable, but is slightly raised and flatly beaked. 

 Under a low power 4 lateral, wavy, longitudinal, olivaceous 

 bands are easily seen ; one valve has six of these bands on 

 either side. When disarticulated and cleaned and seen under 

 a high power some additional markings are revealed. The 

 dorsal and pleural areas are very distinct from the lateral, 

 being covered with longitudinal wavy lines of a pale green 

 tinge ; these to a certain extent merge into one another, giving 

 the reticulate appearance before referred to. This system of 

 marking also covers the broad and flat beak; the broad inter- 

 spaces are white. The lateral area is evenly covered with pale 

 greenish spots, which suggest small pustules, but I am unable 

 to discover any rising in the shell. In some lights, especially 

 daylight, the white interspaces look like white spots and the 

 olivaceous markings like interspaces. The sutural laminae 

 are large, produced to about half the width (longitudinal) of 

 the shell, and separated by a wide sinus; teeth fairly sharp, 

 not rounded as in the anterior and posterior valves, and I can 



