POLLICIPES. | 5] 
2. Poutuicrees oourticus. Tab. III, fig. 2. 
PoLLIcIPEs ooLiticus. Buckman. Outline of the Geology of Cheltenham, by Sir R. 
Murchison, new edit. by James Buckman and H. Strickland, 1845, Tab. iii, fig. 7. 
P. scutis triangulis ; superficie undulaté ; margine basali rectangulé ad marginem rectum 
tergo-lateralem posito ; segmentum tergo-laterale a liners refleais increments formatum deest. 
Carind pene rectd, semicylindricd, margine basali quadrato. 
Scuta triangular ; surface undulatory; basal margin at right angles to the straight 
tergo-lateral margin ; there is no tergo-lateral segment formed by upturned lines of growth. 
Carina nearly straight, semicylindrical, with the basal margin square. 
Stonesfield Slate, Lower Oolite: Eyeford. Mus. Buckman, and Geolog. Soc. 
My materials consist of several scuta, terga, and carine, kindly lent me by Professor 
Buckman, and of another set (which includes the rostrum) presented by him to the 
Geological Society of London. | 
Valves: these have a smooth surface, but are undulatory in the direction of the lines of 
growth ; at the cessation, apparently, of each zone of growth, there was a tendency to form 
a projecting ridge or plait, as takes place in a far more marked manner in some of the 
eretaceous species, namely, P. elegans and fallax. There are also excessively fine, longitu- 
dinal strie, which can be seen only when the valves are held in particular lights; these 
seem to have been formed by the so-called epidermis, which we know in the recent P. 
mitella is longitudinally and finely ribbed. Scwta (fig. 2, c) but slightly convex ; triangular ; 
basal margin straight, forming a right angle with the tergo-lateral margin, and rather less 
than a right angle with the slightly arched occludent margin; the tergo-lateral margin is 
straight, and not at all protuberant: in the figure the left hand is, as usual, the occludent 
margin; I mention this because the valve has a reversed appearance, owing to the unusually 
small angle which the occludent makes with the basal margin. Terga (fig. 2, d) rhom- 
boidal, slightly convex, with a rounded ridge, which is central, running from the apex 
to the broad, rounded basal angle; the upper carinal and occludent margins stand at 
right angles to each other, and are short compared to the scutal and lower carinal margins ; 
there is no trace of a depression parallel to the occludent margin. Carina (fig. 2, a, 6) 
elongated, triangular ; scarcely at all bowed inwards ; not even swé-carinated; basal margin 
rounded, not at all protuberant. The Rostrum differs from the carina only in its greater 
breadth compared to its length. 
Dimensions. The largest scutum is °6 long, but as there is a broken tergum about 1:1 
long, no doubt the species attained a rather large size; the longest carina is *7 in length. 
Diagnostic characters. This species is best characterised by the straightness of the whole 
tergo-lateral and of the basal margin of the scuta; by the ridge being central on the terga; 
by the carina not being carinated; and by the smuous state of the surface of the valves, 
intermediate between the smooth species and those with distinct ridges parallel to the zones 
