184 Mr. T. H. Withers on f^ome 



inwards. Outer yurface ornamented with strongly marked, 

 raised, transveisse ridges, crossed by well-marked longitu- 

 dinal ridges. On the inner surface the occludent edge is 

 very broad and flat, is widest adjoining the pit for the 

 adductor muscle, being more than half the breadth of the 

 valve, and is marked with growth-lines. An elongately- 

 tiiangular furrow, marked with growth-lines, is situated 

 al)Ove the pit for the adductor muscle, and is bounded by 

 the upper part of the inner occludent edge, and this furrow 

 serves for the reception of the scutal angle of the tergum. 



Tergum (PI. VII. fig. 8) subrhomboidal, slightly convex 

 transversely, with an almost straight, wall-sided ridge, much 

 narrower than that of the scutum, extending from the apex 

 to the ba-al angle, where it is produced and truncated > 

 apical portion scarcely curved towards the scuta. The apico- 

 basal ridge is situated almost centrally, and where crossed 

 by the transverse ridges is produced into sharp points. 

 Upper carinal margin slightly convex, and the occludent 

 margin slightly concave, both being about the same length, 

 and shorter tiian the lower carinal and scutal margins, which 

 also are of about the same length. A portion of the valve 

 is rounded and protuberant along the occludent margin, to 

 the extent to which the valve was overlapped by the scutum ; 

 this rounded margin is followed by a wide depression 

 bounded by a more or less distinct ridge extending from the 

 apex to about the middle of the scutal margin. On the 

 inner surface the upper carinal edge is flat, and the inner 

 occludent edge rounded and narrower, both edges being 

 u.arked with growth-lines. 



Tlie upper latus (PI. VII. fig. 7) has the shape of a very 

 acute-angled isosceles triangle. Externally it is marked with 

 irregular, undulating, raised transverse ridges, abruptly 

 upturned at the outer margins ; these ridges are crossed by 

 prominent longitudinal ridges which give to them a goftered 

 ai)pearance. Ihe growth-lines are continued on the inner 

 surface and meet on a raised, sliarp-edged, median ridge, 

 which extends to the apex ; this ridge fitted between the 

 scuta and terga, the valve on either side overlapping the 

 scutum and tergum, while the smooth triangular part at 

 the base was covered by the corium or membrane lining the 

 ins.de of the valves. 



Pycnolepas parunai, de Alessandri, sp. 

 (Plate VII. figs. 1-4.) 



189o. Pollicipes paronai, de Alessandri, Boll. Soc. Geol. Ital. vol. xiii. 

 p. 2UU, pi. i. figvs 6 a-f. 



