11)4 J\Ir. T. H. Withers on some 



to jiidjic from the lenotli of tlie valves known to me, the 

 capitiihuii unist have attained a length of at least 35 mm. 

 Dr. Briinuich Nielsen (1912, pi. i. fig. 13) gives a figure of 

 a tergum, which measures 30 mm. in length, although the 

 apex of the specimen is slightly broken, and his scutum 

 (pi. i. tigs 4-5) has a length of 197 mm. The carina here 

 figured (PI. Vlll. fig. 12) would, if complete, measure quite 

 30 mm. (it now measures 27 mm.). The valves of the lower 

 whorl and the larger of the peduncular plates here figured 

 (IM. Vlll. figs. 16-23) measure respectively : — 



Length. Breadth, 



mm. mm. 



Rostrum 4-2 39 



, Rostral latiis (right) 3-7 5-0 



Median latus 3-8 4'3 



Subcarina 2'6 3-4 



Cavinal latus 2-3 2-5 



Peduncular plate 1'7 I'l 



The largest rostral latus is that figured by Dr. Nielsen 

 (1912, pi. i. figs. 6-8) as a carinal latus, which has a length 

 of 5 mm. and a breadth of 8"5 mm. 



Scutum (PI. VIII. figs. 14, 15) triangular, with the basi- 

 lateral angle widely truncated, considerably convex, breadth 

 about three-quarters the length, apex acute, and oidy slightly 

 cui'vcd towards the terga. Occludent margin slightly convex, 

 forming rather less than a right angle with the slightly 

 convex basal margin. Tergo-lateral margin usually slightly 

 concave; a narrow slip is formed along it by the upturned 

 growth-lines, and this is al)ruptly bent inwards, the inner 

 margin of it forming a sharp ridge on the inner surface. 

 The margin of the truncated basi-lateral angle is almost 

 half the width of the basal margin in the larger valves. 

 Along the occludent margin a narrow portion of the valve is 

 raised to form a rounded ridge, and two further ridges 

 extend from the apex — one to a point about midway on the 

 basal margin, and the other, which is rather less pronounced, 

 to the lowest point of the truncated basi-lateral angle. On 

 the inner surface there is a deep pit for the adductor muscle; 

 the inner inturned tergal edge is concave, and evidently 

 served for the reception of the tergum ; the inner occludent 

 edge is of the same width throughout. Above the pit for 

 the adductor muscle, theie is a triangular depression, 

 bounded by the im.er edges of the tergal and occludent 

 niariiius. 



