Fossil in Coralline Crag (Sutton), Mus. S. Wood.
I owe to Mr. Wood the inspection of a fine suite of separate valves. Owing to the shell never having been found entire, its general shape is not known, and, what is of more consequence, the relative proportional width of the parietes of the carino-lateral compartment is unknown. I have (but with doubt) given it a distinct specific name, owing to the peculiar character of the furrows on the scuta, and to the large size of the whole shell. In its other characters it comes nearest to [A. spongites], excepting in the spur of the tergum, which resembles that of [A. sulcata].
The compartments appear to have been rather smooth externally. The radii are not wide, as in [A. cyathus]; and the basis is cup-formed. Internally, the parietes are feebly ribbed, as in [A. spongites]. Judging from the dimensions of the separated valves, this species must have equalled and perhaps exceeded the size of the largest living species, namely, [A. glans], from Australia. Hence we may infer, that the basal diameter probably exceeded .55 of an inch: I may add, that the largest European specimens of [A. spongites], from Naples and Portugal, are only .3 of an inch in basal diameter.
Scuta.—These seem to resemble the scuta of [A. spongites] in all respects, except in the longitudinal ridges standing much further apart, and, consequently, in the furrows being much wider: each ridge is generally double. Although there is a good deal of variability in the character of these ridges in [A. undulata], and likewise in [A. spongites], I have not seen any form intermediate between them. It must, however, be confessed, that this is an extremely variable character in many sessile cirripedes. In the Terga, the spur is about half the width of the whole valve, and therefore rather wider than in [A. spongites].
5. [ACASTA] GLANS. Pl. [9], fig. [5 a]-[5 c].
ACASTA GLANS. Lamarck. Animaux sans Vertèbres, 1818.
Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge rarely crenated, but furnished with six inwardly prominent teeth: scutum strongly striated longitudinally.
Var. (a) with the edge of the basal cup finely crenated.
Hab.—New South Wales, Southern Australia; Mus. Brit., Stutchbury, &c.