51 



third the height of the shell from the hinge hne ; below the sinus obliquely 

 rounded backwards along the ventral margin to the lower posterior angle 

 which is somewhat narrowly rounded. The posterior wing is large and 

 much compressed ; the angle about 90^ ; below which the outline is 

 slightly concave for about one-third the height and then convex to the 

 lower posterior angle. The beaks appear to be rather large, closely 

 incurved and situated about one-fifth of the whole length of the hinge 

 line from the anterior angle. The left valve is obliquely and rather strongly 

 convex, the body of the shell (or the convex portion excluding the wings) 

 narrow. The right valve is moderately convex and in one specimen nearly 

 flat. Surface of left valve with fine radiating striae, about two in one 

 line, crossed by finer sub-lamellose concentric striae. There are also 

 some concentries undulations of growth. Surface of right value with 

 strong concentric, concave undulations of growth about one line wide each : 

 and perhaps also radiating striae, but the specimens do not show any of 

 these latter. Length of the largest specimen seen, on the hinge line, 15 

 lines ; height 12 lines. 



The difference in the surface characters of the two valves is so great 

 that they -would not be regarded as belonging to the same species unless 

 in place. One specimen free from the matrix and with the valves in 

 connection was collected. Gamache Bay ; Div. 1, A. G. T. C. Weston. 



P. CDRIOSA, n. sp. — The specimen on which this species is founded has 

 both valves in connection and is perfectly detached from the matrix but it 

 is not certain that the whole of the margin is preserved so that the follow- 

 ing description may not give the true outline of the perfect shell. The 

 left valve is rather strongly convex with a moderately compressed posterior 

 wing. Hinge line straight, six lines in length ; beak of left valve small, 

 pointed, incurved over the area and situated nearly two hnes from the 

 anterior extremity of the area ; the latter apparently concave, one line in 

 height at the beak. That part of the shell which lies below a Ime drawn 

 across two lines below the area is a triangle of which the two lower sides 

 are gently convex and meet to form an obtuse rounded angle of about 

 110°. This angle is situated a httle in front of a line drawn vertically 

 downwards at a right angle from the mid-length of the area of the right 

 valve. Above the Hne (drawn across the shell) the anterior extremity 

 slopes towards the beak ; the posterior extremity rounded to the hinge- 

 line. Distance from the middle of the area of the right valve to the angle 

 on the ventral margin nearly seven lines ; width of the shell on a line two 

 lines below the area eight lines ; from the beak of the left valve to the 

 ventral angle eight lines. 



The right valve is gently convex. The shell appears to be very thin 

 and with fine concentric striae on the left valve which on approaching the 



