POLLICIPES. 69 
of all the valves, as far as is apparent, being downwards, and from their number, appa- 
rently exceeding 16, I have, without hesitation, ranked this species, (and consequently 
P. glaber,) under the genus Pollicipes. 
scuta being exteriorly strengthened by a prominent ridge, and by the two angular ridges running down to 
the basal margin, and by the general character of the under surface of the apex: it differs widely from P. 
dorsatus, in the rostral, tooth-like process, and in the baso-lateral angle not being widely truncated. The 
carina of these two species also present some points of similarity. In P. validus the centre of the upper 
freely projecting portion often, but not always, has a longitudinal crest or ridge: in the recent P. mitella, 
the degree of filling up of the upper part of the carina varies considerably, and sometimes even a central 
crest is formed in it. 
14, PoLicrprs eRaciLis. Tab. IV, fig. 3. 
PoLLICIPES GRACILIS. Roemer. Norddeutsch. Kreidegebirges, 1841, Tab. xvi, fig. 14. 
P. scutis tenuibus, angustis, margine occludente externé costd rotundatd Jirmato ; intus prominentid 
rostrali infra marginem basalem dependente ; costd ab apice ad marginem basalem centrali : interne, sulco 
transverso super fossam musculi adductoris, excavato. 
Scuta thin, narrow, occludent margin exteriorly strengthened by a rounded ridge ; internally at the ros- 
tral angle a blunt tooth depends beneath the basal margin; the ridge running from the apex to the basal 
margin is central. Internally there is a transverse furrow above the hollow for the adductor muscle. 
Unterer Kreidemergel (lower division of Lower Chalk), Hanover. Oberer Kreidemergel, Shaftricht. Mus. Roemer. 
Roemer has most kindly sent me a beautifully preserved scutum, which he has fully described in the above 
quoted work. It is unfortunately rather young, being ‘6 of an inch in length. It resembles so closely 
the same valve in P. validus, that had it not already received a name I should not have affixed one; still [ 
think it is perhaps a distinct species. -It will be quite superfluous to do more than describe the few points 
of difference, of which the chief and most conspicuous one is the much greater thinness of the whole valve. 
I should, however, state that I have not seen any specimen of P. validus so small, the smallest being more 
than one third longer. The second chief difference is that the medial longitudinal ridge here runs to a 
central point of the basal margin instead of to a point nearer to the rostral angle. I think the basal margin 
is more conspicuously formed by two distinct lines, meeting each other at the above point. Internally the 
third and perhaps most important distinction is the presence of a moderately deep and large depression or 
fold, marked by lines of growth, extending inwards from the occludent margin, just above the pit for the 
adductor muscle, and as far inwards at the middle of the pit: this fold precisely resembles that which 
occurs in the same position in Scalpellum magnum, vulgare, and in some Pollicipes, as P. Angelini. The 
rostral tooth appears to have been larger. Owing to the thinness of the valve, the internal occludent edge 
does not here present a flat striated ledge. 
I must again repeat that I doubt whether the differences here pointed out are specific: I have seen nearly 
all such peculiarities variable in other species. I am, however, in some degree strengthened in leaving the 
P. gracilis distinct, by the supposition that it is the representative species in the true Chalk of the P. 
validus of the uppermost stage. 
15. PoLLICIPES DORSATUS. 
PoLiicipEes DorsaTus. Steenstrup. Kroyer’s Naturhist. Tidsskrift, 1839, b. ii, h. iv, pl. v, figs. 27 and 30. 
P. seutis crassis; ad formam trianguli equianguli accedentibus ; margine occludente externé costd 
rotundatd firmato ; angulo baso-laterali late truncato, dimidium longitudinis marginis basalis veri, equante ; 
