~SCALPELLUM. - 25 
point from the lateral margin, which in the lower half is slightly protuberant; tergal 
margin straight, with the edge thickened and slightly reflexed. A distinct, square-edged 
ridge (therefore formed by two angles) runs from the umbo to the baso-lateral angle, which 
is itself obliquely truncated. Internally (/), there is a large and deep pit for the adductor 
scutorum. erga (fig. 44) triangular, flat, large, fully one third longer than the scuta; 
basal half much produced ; basal angle pointed; from it to the apex or umbo there runs 
a narrow, almost straight furrow, at which the lines of growth converge—it runs at about 
one third of the entire width of the tergum (in its broadest part) from the carinal margin. 
Parallel to the occludent margin, and at a little distance from it, there runs a wide, very 
shallow depression up to the apex. ‘The scutal margin is not quite straight, about a third 
part, above a slight bend corresponding with the apex of the upper latera, being slightly 
hollowed : from the above bend a very faint ridge runs to the apex of the valve. Upper latera 
(fig. 4 2) large, flat, with five sides, of which the two upper are much the longest; the 
basal side is next in length, and the scutal side much the shortest. As far as I can judge 
of the positions of the lower valves, with respect to the upper latus, I believe, that the 
rostral latera, probably, abutted against the shortest of the three lower sides; that the 
carina ran along the one next in length, and the carinal latera along the middle basal 
side, which I suppose extended in an oblique line, and not parallel to the base of the 
capitulum: the two upper long sides no doubt touched the scuta and terga. The umbo 
of growth is at the apex; there is, however, a trace of a projecting ledge added round the 
upper margins during the thickening of this upper part of the valve. T'wo slight ridges run 
from the apex to the two corners of the middle of the three lower sides. Carinal latera 
(fig. 4e): these are not quite perfectly seen: the umbo forms a sharp point, whence the 
valve rapidly expands and curves apparently downwards and towards the upper latera. 
Near one margin there is a very narrow furrow, and on the other a wide depression, both 
running and widening from the umbo to the opposite end, which is slightly sinuous. I 
imagine these carmal latera occupied a nearly triangular space between the middle of the 
three lower sides of the upper latera and the basal portion of the carina. ostral latera, 
rostrum and peduncle unknown ; the rostral latera must have been very narrow. 
Affinities—In the shape and manner of growth of the scuta, and more especially of 
the upper latera, this species is certainly more closely allied to the eocene S. guadratum, 
than to any other species; but in the peculiar characters of the carina, it is nearer to the 
recent S. rutilum ; we have previously seen that the nearest congener to S. guadratum is 
this same S. rutilum. The most conspicuous diagnostic character of this species is derived 
from the peculiar form of the carina,—its tectum bemg bounded by a rounded ridge on 
each side. The square-edged ridge running from the apex to the baso-lateral angle of 
the scuta is a trifling, but I believe, a diagnostic character. If I am right in placing 
S. rutilum mm the genus Scalpellum, and I think there can be no doubt of this, considering 
the characters of its complemental male, then there can be no on that the present 
species belongs to the same genus. 
d 
