44 FOSSIL CIRRIPEDIA. 
The valves all have their surfaces plainly ribbed longitudinally ; the ribs are narrow, 
and as they cross each zone of periodical growth they are tuberculated. 
Carina (fig. 10, 6, c); narrow, tapering, little bowed inwards ; tectum in a transverse line, 
steeply arched, not cariated; basal margin bluntly pointed; in very young specimens, 
however, it is evident from the lines of growth, that the basal margin must have been 
rounded ; the parietes are inflected, and rather narrow, being barely half the width of 
half the tectum; they are plainly marked by parallel lines of growth; internally the valve 
is rather deeply concave; no part of the apex projected freely. 
Scuta (fig. 10, e); umbo of growth on the occludent margin, at about one third of the 
entire length of the valve from the apex; somewhat convex; four-sided, the margins 
consisting of the lateral, which is considerably longer than the other sides; the basal 
which forms nearly a right angle with the lower half of the occludent margin; and 
of an upper and lower occludent margin, meeting each other at about an angle of 135°: 
the margin which I have here called the upper occludent, homologically corresponds with 
the tergal margin of the other cretaceous species, and with the upper, nearly straight, 
portion of the occludent margin in the tertiary S. magnum and the recent S&. vulgare,— 
a fact which has been mentioned under the head of Scalpellum. The edge of the upper 
occludent margin forms a strongly prominent ridge, with its apex forming a slight pro- 
jection ; a second less prominent ridge runs from the umbo to the baso-lateral angle, and a 
third faint ridge runs from the umbo to a point in the basal margin, nearer to the rostral 
than to the baso-lateral angle. Internally there is a rather deep hollow for the adductor 
muscle; along the under surface of the upper occludent margin there is a slightly 
prominent ridge, bordered by two slight depressions. 
Terga (fig. 10, a); flat, elongated diamond-shape ; close and parallel to the occludent 
margin there is a narrow, very prominent ridge or plait, the end of which forms a slight 
projection; a straight ridge runs from the apex to the sharp basal angle; the scutal and 
lower carinal margins are of equal length, and longer than the occludent and upper carinal 
margins, which latter are equal, and meet at an angle very slightly less than a rectangle. 
On the under surface there is a slight depression and ridge, close and parallel to the 
occludent margin. I have no doubt that the ridge along the upper oceludent margin of 
the scuta, and that on the occludent margin of the terga, together with their projecting 
points, are related to each other, owing to the close contact of these valves,’ 
1 14. ScaLPELLUM sEmrporcatuM. Tab. I, fig. 6. 
S. carind ignotd: scuti costis duobus ab umbone ad angulum basi-lateralem et ad marginis basalis 
medium decurrentibus : superficie inter hanc costam et marginem occludentem lineis tenuibus, longitudinalibus, 
elevatis instructd. 
Carina unknown: scutum, with two ridges running from the umbo to the baso-lateral angle, and to 
