SCALPELLUM. 29 
a narrow ledge of about equal width with the occludent edge, marked likewise with lines 
of growth, must have overlapped the tergum. Largest specimen 1°15 in length. 
Scutum, Var. I, Tab. Il, fig. 9. This valve is narrow, moderately convex, with the 
upper portion much acuminated; the tergal margin is somewhat hollowed out, and is 
bordered by a narrow smooth slip, (as in the scutum of S. arcuatum,) which is simply 
formed by the thickenmg from within of the upper part of the valve; this slip does not 
reach to the uppermost point. The occludent margin is somewhat arched, at nearly right 
angles to the basal margin; lateral margin forming an angle a very little above a right 
angle with the basal margin. A conspicuous, curved, angular ridge runs from the 
apex to the baso-lateral angle, (which is not at all protuberant,) and divides the valve 
obliquely into two almost equal halves. Surface just perceptibly striated, finely and 
longitudinally. Internally there is a deep pit for the adductor scutorum, which is situate 
low down in the valve; the imner occludent edge in the upper part of the valve (4), above 
the adductor scutorum, widens suddenly, and is formed into a furrow, which, however, 
I do not believe to have had any functional importance; the central internal surface 
of the valve, above the pit for the adductor muscle, is somewhat prominent; and a 
quite small, almost flat, portion of the tergal side is marked by lines of growth, showing 
where it overlapped the tergum. Altogether there is a considerable resemblance between 
this valve, both externally, and more especially internally, and that of the Pollicipes 
Angelim. ¥rom the valve bemg acuminated, with the upper part rather solid, and from 
the surface bemg just perceptibly striated, it more probably belonged to var. swlcatwm than 
to the typical 8. maximum. 
Scutum, Var. 111, Tab. II, fig. 10. This third variety, of which the specimen is a fine 
large one, is about intermediate in outline or -acumination between the first and second 
varieties: the tergal margin is thickened and reflexed as in the first, and is not bordered 
by a smooth narrow slip as in the second variety. There is no distinct angular ridge, as 
in the second variety, running from: the apex to the baso-lateral angle. Internally the 
differences are more conspicuous; the depression for the adductor muscle is pretty well 
developed; a large portion of the upper part of the valve projected freely; the mternal 
occludent edge, above the adductor-depression, becomes greatly widened and deeply 
hollowed out, but yet the furrow I believe, as in Var. II, to be of little or no functional 
importance, and merely a consequence of the internal thickening of the central upper part 
of the valve; on the tergal side a wide ledge shows the extent to which that margin 
overlapped the tergum. The internal surface of the valve, above the adductor-depression, 
is filled up solid and is exceedingly prominent, as is the ridge extending from it to the’ 
apex ; this ridge, from the unusual width of the internal occludent edge, is pushed over to 
the tergal side of the valve. 
Professor Steenstrup has sent me two small scuta, collected by M. Angelin at Kopinge 
and Balsberg, in Scania, which come near to the Third variety; the internal furrow, however, 
along the occludent margin, is much narrower, deeper, and oblique, so that it is partly 
