SCALPELLUM. 23 
were probably attached. TZerga (fig. 3 c) triangular, large, flat, basal angle bluntly 
pointed; apex slightly projecting, as a solid horn ; occludent margin very slightly arched. 
Rostrum unknown; judging from the narrowness of the umbones of the rostral latera, 
it was probably minute or rudimentary. Upper latera (fig. 3 e) large compared with 
the lower valves, flat, five-sided, with the two upper sides the longest; of the three lower 
sides, that corresponding with the end of the rostral latera is generally (especially in 
young specimens) the shortest. Umbo seated at the uppermost angle; but in full-sized 
specimens, a narrow ledge has been added, during the thickening and growth of the valve, 
along the two upper margins, and consequently round the apex. Rostra latera (fig. 3/) 
extremely narrow, three or four times as long as wide; considerably arched, extending 
parallel to the basal margin of the scuta; widening gradually from the umbo to the 
opposite end, which is obliquely truncated in a line (as I believe) corresponding with the 
shortest side of the upper latera ; inner surface smoothly arched ; during growth, the narrow 
rostral half of the valve becomes much thickened, and at the same time added to along its 
upper margin, thus producing a solid, sloping, projecting edge ; umbo slightly projecting. 
Carinal latera (fig. 3.g) almost flat, not elongated, of a shape difficult to be Seog 
approaching to a triangle, with curved sides, and one angle protuberant. 
Peduncle. he calified scales are apparently large in proportion to the valves of the 
capitulum ; transversely elongated, pointed at both ends, and more or less crescent shaped. 
_ Affinities. This species was generically separated from Scalpellum by Mr. Dixon, as I 
am informed by Mr. James Sowerby, solely owing to the umbo of growth in the carina 
being at the apex, instead of being sub-central, as in S. vulgare; but I need not here 
repeat the reasons already assigned for at present keeping all the recent and fossil species 
under the same genus. In the umbo of growth, in the carma and scuta being seated at 
their upper ends, in the square form of the carina, in there being only three pair of latera, 
and in the large size of the upper latera, this eocene species is much more closely allied to 
S. rutilum (nov. spec., of which the habitat is unfortunately not known,) than to any other 
recent species. In some respects, however, I may remark, S. rutilwm is even more closely 
related to certain cretaceous forms. To S. ornatum, the nearest recent congener of S. rutilum, 
the present species is allied by the narrowness of the rostral latera, and by the large size 
and peculiar shape of the scales on the peduncle: the carinal latera perhaps rather more 
resemble those of S. vulgare than of any other recent species. Certainly, all the affinities 
in S. quadratum point to S. rutilum, ornatum, and vulgare, and these three recent species 
are characterised by having males or complemental males attached to the sides of the orifice 
of the sack, whereas, in the other species, they are elsewhere attached; hence it is that I 
believe that males were probably lodged in the slight depressions described on the inner 
sides of the scuta; but the depression is not here nearly so distinctly developed as it is 
in the recent S. ornatwm, and more resembles the fold on the occludent edge of the valve 
in S. vulgare: 1 must add that folds of this nature do not necessarily imply the presence 
of males. 
