20 FOSSIL CIRRIPEDIA. 
will be seen how closely the two valves resemble each other. The scutum of §. tubercu- 
latum (fig. 10d) is intermediate in its manner of growth between those of S. magnum and 
fossula. Internally, the impression for the adductor muscle is deep! on the occludent 
margin, close to the umbo, there is a deep fold, which is connected with the growth of the 
upper part of the valve being subsequent to that of the lower part. There is very little 
difference between this valve and that of 8. vulgare ; the upper part, however, appears to 
be always thicker. Length of largest specimen one eighth of an inch. 
Terga (fig. 1 d) triangular, sometimes approaching to crescent-shaped; flat and thin, 
though the thickness of the valve varies. Carinal margin straight, or very slightly hollowed 
out; in its upper part there is a barely perceptible prominence marking the limit of the 
upward extension of the carina. Basal angle blunt, rounded ; from it a line, formed by the 
convergence of the zones of growth, runs near and parallel to the carmal margin, up to 
the apex. Occludent margin about equal im length to the scutal; parallel to the former, 
a slip of the valve is rounded and slightly protuberant, and this portion projects a little on 
the scutal margin. A very small portion, or none, of the apex of the valve projected freely. 
This valve is somewhat narrower, and the scutal margin straighter than in 8. vulgare. 
Rostrum unknown, no doubt rudimentary, probably quadrangular. 
Upper latera (fig. 1 e) flat, oval, with the upper half a little pomted; the lower margin 
shows traces in a varying degree consisting of three sides. The surface, but chiefly of the 
lower half, is faintly marked with strize radiating from the centre. ‘The umbo lies in the 
middle, and from it two slight ridges, first bending down, diverge on each side. In Scal- 
pellum vulgare this valve (which is very similar in shape to that of S. magnum) at the first 
commencement of its growth, as with the scuta, is added to only downwards; and thus the 
two diverging ridges mark the form which the valve originally tended to assume: bearing 
in mind that the basal margin tends to be three sided, if we remove that part of the valve 
above the ridges which have been superadded to the original form, we shall have a five- 
sided valve, essentially like that in the 8. guadratum and S. fossula (fig. 3 e, and fig. 4d). 
Rostral latera (fig. 1, g to &) elongated, widenmg gradually from the umbo to the 
opposite end, which is equably rounded: umbonal half free, curling outwards ; the internal 
surface of the other half (4) is nearly flat and regularly oval, with its end towards the umbo 
pointed ; the freely projecting portion varies from nearly one half to one third of the entire 
length of the valve; but in one distorted specimen it was only one sixth of this length. 
The width, also, of the valve varies (y and 4), compared to its length. This valve, com- 
pared with its homologue in S. vulgare, differs more than any of the preceding valves; it 
is proportionally larger, and the internal or growing surface is oval, instead of being oblong 
and almost quadrangular; and the umbonal or freely projecting portion in 8. vulgare is 
only one sixth or one seventh of the entire length of the valve. 
Infra-median latera wnknown. 
Carinal latera (fig. 1, 7 to) narrow, thick, much elongated, widening gradually from 
the umbo to the opposite end, which is rounded and obliquely truncated. Surface, exteriorly 

