SCALPELLUM. 21 
flat; internally convex. The umbonal, freely projecting portion is sometimes more than 
half, sometimes only about one third, of the entire length of the valve. ‘This portion curls 
outwards and likewise upwards. ‘The degree of curvature and the width (m and x), in pro- 
portion to the length, varies. The upper and lower margins are approximately parallel to 
each other ; the umbonal end of the growing surface is bluntly pointed. This valve differs 
from its homologue in S. vu/gare, in being larger, much narrower in proportion to its length, 
more massive, and with a far larger portion of the umbonal end freely projecting ; also in 
the approximate parallelism of the upper and lower margins, and in the umbonal end of the 
growing surface being pointed instead of square. In S. vulgare the upper margin is much 
more curled upwards than the lower, and the freely projecting portion is only one fifth of 
the entire length of the valve. 
Taking the largest specimens in Mr. Wood’s collection, the freely projecting portions 
of the carinal latera must have stuck out like horns, curling from each other and a 
little upwards, for a length of a quarter of an inch. So again, the much flattened horns of 
the rostral latera, curving from each other, but not upwards, must have projected half an 
inch beyond the probably rudimentary rostrum. The capitulum must have presented a 
singular appearance, represented in the imaginary restored figure (fig. 1 a), with its pair of 
projecting horns at both ends. 
Peduncle ; calcareous scales unknown, but undoubtedly they existed. 
Varieties: the variation in the rostral and carinal latera has already been pointed out. 
In Mr. Wood’s collection there are numerous scuta, terga, carinee, and carinal latera, 
from Sutton; and these are all smaller than those above described, which come from 
Sudbourne, and than some others in Sir C. Lyell’s collection from Gedgrave. All these 
places, however, belong (as I am informed by Mr. Wood) to the same stage of the Coralline 
Crag. In the Sutton specimens the carinal latera show the same character as in those from 
Sudbourne, but the carina apparently is not internally so much narrowed in under the 
umbo ; this, however, is a character which is conspicuous only in the larger Sudbourne 
specimens, and anyhow cannot be considered as sufficient to be specific. 
I may take this opportunity of stating, that in Mr. Harris’s collection of organic remains 
from the chalk detritus, at Charing, in Kent, I have found the upper part of a carina of 
a very young and minute Scalpellum, which cannot be distinguished from this species ; 
but considering the state of the specimen, it would be extremely rash to believe in their 
identity. All the known cretaceous species have the umbo at the apex, so that the Charing 
specimen differs remarkably from its cretaceous congeners. 
