POLLICIPES. 63 
Northfleet, present some slight differences, in the valve being flatter, in the tergo-lateral 
portion being more developed, and in the basal margin being straighter ; but these differ- 
ences are so very slight that it would be exceedingly rash to consider them as specific. 
Terga (fig. 10, e, a) ; rhomboidal, flat, with a straight slight ridge running, at about one 
third of the entire width of the valve from the carinal angle, to the sharp basal angle ; this 
ridge is steep on its carinal side, on which side the whole surface of the valve is somewhat 
depressed. ‘The upper carinal margin meets the occludent margin at somewhat less than a 
right angle: the occludent margin slightly exceeds in length the scutal margin; the valve 
is widest nearly in its middle. A narrow rim along the occludent margin is slightly pro- 
tuberant, within which there isa slight parallel depression. The scutal margin is not quite 
straight ; the lower half (which probably was in contact with the upper latus) projecting a 
little. 
Carina (fig. 10, 7, g); triangular, tapering, moderately strong, with a smooth surface ; 
almost straight or slightly curved inwards; transversely, flatly arched, sub-carinated. 
Lateral margins narrow, inflected, with the lines of growth first curved downwards (y), 
and then on the edge itself abruptly upturned; basal margin bluntly pointed, apparently 
in a variable degree. The two baso-lateral angles are slightly prominent, in conformity 
with the above-stated direction of the lines of growth along the margin. I may remind 
the reader that this valve, the terga, and the latera presently to be described, were all 
embedded together in their proper positions. 
Rostrum (fig. 10, 4, 7): in Mr. Flower’s collection, with the other loose valves from 
Stoke Ferry, there is one which I can hardly doubt is a rostrum: it is nearly an equilateral 
triangle ; externally convex, sub-carinated, basal margin not protuberant. The upper part, 
for about one fourth of the entire length of the valve, must have projected freely ; this 
part is remarkable, from having been filled up internally with a central crest, like the carina 
of P. validus and carinatus. 
Upper latus (fig. 10, &, a); flat, almost an equilateral triangle, but with the two upper 
sides not exactly equal, and both a very little longer than the basal margin; umbo 
of growth at the uppermost point; length, one third of the terga; surface smooth, with no 
trace of a central longitudinal ridge; internally the edges are bevelled, and a very small 
portion of the apex must have projected freely. 
Lower latera (fig. 10,7, a). There are two of these (one much broken) nearly resembling 
each other: from analogy with the latera of P. wngwis, these are probably from the rostral 
end of the capitulum; they are slightly convex, and approximately form a transversely 
elongated triangle, with one corner cut off; the two upper sides are slightly unequal in 
length: umbo of growth at the apex, from this point a narrow well-defined ridge runs 
obliquely across the valve, to the most protuberant point of the basal margin, which is 
situated about one fourth of the entire width of valve from one end. ‘These lower latera 
are wider than, but not so high as the upper latus : seen internally the edges are bevelled, 
and a very small portion of the apex must have projected freely. 
As it is so very rare to find the valves of a Pollicipes united, it will be advisable to give 
