24 T. H, Withers — Cirripedesfrom the Chalk. 



and basal angle pointed. Carinal margin slightly extended for its upper third beyond 

 the rest of the margin, and forming a narrow, almost rectangularly inflected margin, 

 which when looked at from above is hardly discernible, so that the whole carinal 

 margin appears to be nearly straight. Scutal margin slightly sinuous, a little 

 longer than the occludeut margin, with which it forms an obtuse angle. Am 

 obscure ridge divides the valve unequally from the apex to the basal angle. 

 Carinal portion very narrow, wider in its upper third, and ornamented with two or 

 three extremely line longitudinal lines. Occludent portion at its maximum much 

 wider than the carinal portion, and with raised ridges radiating from the apex. Of 

 these ridges, two are much coarser than the others, one extending from the apex to 

 about the middle of the scutal margin, and the other, which is much more raised, 

 running near and almost parallel to the occludent margin. Inner surface of valve 

 shows more plainly the abrupt extension of the upper third of the carinal margin. 

 From the base of the projecting portion to the apex, and along its edge, a narrow 

 portion of the valve is marked with fine oblique lines, which are also seen for the 

 same extent on the opposite edge of the valve. For about a third of the breadth of 

 the valve, parallel to the occludent margin and extending nearly its length, the inner 

 surface of the valve is marked with a series of small tubercles. 



Remarks. J. Bosquet (1854), in his original description of the 

 carina of S. Darwinianum, states that the tecta or roof-parts of the 

 carina are smoothed and flattened, the rest of the valve being 

 ornamented with fine ribs. In the English examples, on the contrary, 

 the whole of the valve is covered with raised ridges, these being more 

 strongly marked on the tecta, and this seems to be the case also with 

 the carina from the Actinocamax quadratus-zone of Reims represented 

 in the figure given by A. Peron (1888). The tergum described above 

 also presents slight differences, the most important being the position 

 of the ridge that divides the valve into carinal and occludent portions. 

 Bosquet figures this as situated almost in the middle of the valve, 

 while in the English example it is much nearer the carinal margin. 

 Both terga agree in the presence of a narrow tract of tubercles on 

 their inner surfaces, a character which is not known in any other 

 Cretaceous species of Scalpellum. The function of these tubercles is 

 evidently closely connected with the attachment of the membrane 

 which held together the plates of the capitulum. These differences, 

 however, are not sufficient to justify founding a new species, since 

 the smoothness of the tecta mentioned by Bosquet in his diagnosis 

 of the species, and emphasized in his figure of the carina, may be due 

 to the imperfect or different mode of preservation of the Maestricht 

 specimens. On the other hand, it may represent a different stage in 

 the development, and in this connexion it may be noted that the 

 English and Erench forms come from a slightly lower horizon. 



The carinas of this species are very variable, the ribs in some 

 specimens being much finer and more numerous than in others. This 

 is also the case with two carinas from the Maestrichtian of St. Pierre, 

 Duchy of Limbourg, which were acquired from the author of the 

 species, J. Bosquet, for the British Museum (Natural History), 

 registered (I 13604, I 13605). The smaller specimen (I 13605) is 

 ornamented with very fine and numerous ridges, the tecta not being 

 very smooth; the larger specimen (I 13604) has much coarser and 

 fewer ridges, and the tecta are much smoother. In the carina 

 (Fig. 3) from Alderbury, the valve is convex on the left side and 

 concave on the right, a feature which can be seen in the larger valve 

 (I 13604). This, however, is not the case in the smaller valve 



