POLLICIPES. 69 



of all the valves, as far as is apparent, being downwards, and from their number, appa- 

 rently exceeding IG, I have, without hesitation, ranked this species, (and consequently 

 F. (/laher^ 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. 

 dorsatiis, 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. Pollicipes gracilis. Tab. IV, fig. 3. 



Pollicipes gracilis. Roemer. Norddeutsch. Kreidegebirges, 1841, Tab. xvi, fig. 14. 



P. scutis tenuibus, angustis, margine occludente externe costd rotundatd firmato ; intus prominentia 

 rostrali infra marginem hasalem dependente ; costd ab ajnce ad marginem basalem centrali : internh sulco 

 transverso super fossam miisculi 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. Mug. 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 I 

 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 jjrecisely resembles that which 

 occurs in the same position in Scalpellum magnum, vulgare, and in some Pollicipes, as P. Augelini. The 

 rosti'al 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. 



Pollicipes dorsatus. Steenstnip. Kroyer's Natnrbist. Tidsskrift, 1839, b. ii, h. iv, pi. v, figs. 27 and 30. 



P. scutis crassis ; ad formam trianguli cequianguli uccedentibus ; margine occludente externe costd 

 rotundatd Jirmato ; angulo baso-laterali latii truncato, dimidium longitudinis marginis basalis veri, cequante ; 



