Professor MacGillivray on the Cirripedia. 299 
The tegmen testaceous, much compressed, ovate, with the base some- 
what oblique and straight, the ventral margin convex, sinuate toward 
the end; the dorsal margin uniformly curved in about the fifth of a 
circle ; the apex obliquely truncate. 
The lower lateral plate little convex, subovato-tetragonal, very thin, 
fragile, white, faintly iridescent, glossy, concentrically rugoso-striate, 
divergently-minutely striulate; the basal margin straight, or slightly- 
concave or convex, the umbonal or basi-ventral angle projecting a little; 
the ventral margin conyex, the dorsal convex scarcely half the length 
of the basal; the sutural margin straight ; the apex rather acute. 
The upper lateral plate oblongo-triangular, flat, somewhat concave, 
very thin, fragile, white, faintly iridescent, concentrically striate, diver- 
gently minutely striulate ; the ventral margin slightly concave ; the su- 
tural margin straight; the dorsal slightly convex, but with the umbonal 
point sensibly projecting, and about half the length of the ventral margin 
from the upper angle, which is rounded; the lower angle narrow, but 
rather obtuse. 
The dorsal plate curved, linear-oblong, convex, with a slight medial 
groove, or obtusely carinate, striate, narrower and incurvate below, with 
a transverse arcuate or semilunar base; the apex obtuse, extending to 
the middle of the lateral plate. 
The epidermis on the margins of the calcareous plates is bright scar- 
let ; between the plates, and at the base of the tegmen, scarlet or orange, 
often inclining to yellowish-grey. 
The peduncle short, about the length of the tegmen, sometimes shorter, 
sometimes half as long again, rugoso-granulate, light greyish-yellow or 
flesh coloured, orange or scarlet, becoming bright scarlet at the upper 
part ; its internal or dermal tube pale greyish. 
Very young individuals, two-twelfths of an inch in length, and others 
up to half an inch or more, haye the peduncle and membranes yellowish- 
white ; the tegmen and its plates of the same form as in the adult, but 
the plates extremely thin, almost membranous at the margins. 
Considerable variations occur in the outline of the tegmen ; in the form 
of the plates, and especially of the upper as well as the dorsal; in the 
thickness of the plates, and the convexity of the lower; and in distinct- 
ness of the striz. 
Generally ovate, the tegmen has its basal line straight, or somewhat 
convex, rarely a little concave ; the ventral line convex for half its length, 
then sinuate or slightly concave; the dorsal line more or less convex ; 
the apex generally obliquely truncate, or obtuse, or even acute. The 
lower plate sometimes has the ridge from the umbo to the point very 
prominent, but generally inconspicuous, its sutural margin generally a 
little concave, sometimes straight. In the upper plate, the umbonal 
angle is sometimes distinct or even prominent, sometimes inapparent, 
whence the apex may be obliquely truncate, or the dorsal line may run 
in a uniform curve to the end, or the tip may even beacute. The dorsal 
piece may be broader or narrower, more or less convex, sometimes nearly 
flat, but generally with an obtuse keel, sometimes having a medial groove; 
One or more series of depressed dots sometimes extend from the umbo 
to the suture-margin of the lower plate, as has been noticed by Chemnitz 
and Philippi. The strie are sometimes very distinct, although fine, 
sometimes faint or somewhat obsolete. 
The bluish tint of the plates is entirely owing to the pigment and 
ig for when they are removed the colour is pure white, or reddish- 
white. 
The application of the term levis, smooth, as specific, by Lamarck 
and others, is improper, inasmuch as the valves are always striate. 
