Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Tergum with the spur not very short, broad as one third of valve.
Fossil in Red and Mammaliferous Crag, England; Mus. S. Wood, Bowerbank, Lyell, J. de C. Sowerby, Henslow, &c. Mammaliferous Crag, Postwick, near Norwich, Mus. Lyell.
This species so closely resembles [B. bisulcatus], both externally and in all the essential characters of the parietes, radii, and basis, that it is quite superfluous to describe over again these parts. The specific characters are derived from the opercular valves, which present well defined distinctions, found by me constant in several specimens of both species. [B. dolosus], like [B. bisulcatus], has quite smooth and deeply plicated varieties, often adhering to the same univalve. The ribs on the inner surfaces of the parietes are remarkably prominent. I think the upper margins of the radii are in this species rather more oblique than in [B. bisulcatus]. The sutural edges of the radii are marked by the finest striæ, representing septa. The sutural edges of the alæ are generally distinctly crenated. The basis is often slightly cup-formed, and very plainly porose: its surface is marked by radiating ridges. The orifice of the shell is large, and elongated, especially in young specimens. The basal diameter of the largest specimen is .4 of an inch.
The Scuta have no trace of the two or three longitudinal furrows so conspicuous on these valves in [B. bisulcatus], and which, in that species, run down from the apex of the valve; this fact showing that the furrows occur in quite young individuals. The whole valve is not quite so narrow as in [B. bisulcatus], but otherwise agrees with it in shape: internally, there is hardly any difference: the articular furrow is not so wide: the articular ridge is very prominent, and abruptly truncated at its lower end: the adductor ridge is also prominent; it here runs a little higher up the valve than in [B. bisulcatus]. The Tergum differs more in the two species: the spur is not so broad; measured in its upper part, it is only about one third of the entire width of the valve, instead of being half as wide as the valve: it is considerably longer, depending beneath the basi-scutal angle more than half its own width: the basal margin of the valve on the carinal side, does not slope so gradually into the spur: the occludent and carinal margins are slightly arched, as in [B. bisulcatus]. Internally, the surface is rough, the articular ridge is prominent, and the crests for the tergal depressores are well developed,—all as in [B. bisulcatus]. It is remarkable, how generally the opercular valves have been preserved in this species in its fossil condition, as compared with most other species of the genus.
It is not easy to distinguish by external characters the rugged varieties of this species from [B. crenatus]; indeed, the only difference is that the furrows receiving the edges of the radii, generally, exhibit in [B. crenatus] a slight impression of the septa, which are entirely absent in [B. dolosus]. By internal characters, such as the non-porose parietes, and porose basis, our present species widely differs from [B. crenatus].
43. [BALANUS] UNGUIFORMIS. Pl. [8], fig. [8 a]-[8 b].
BALANUS UNGUIFORMIS. J. de C. Sowerby (!). Mineral Conchology (sine descriptione) Tab. 648, fig. 1, (Jan. 1846).
------ ERISMA. J. de C. Sowerby (!). Ib., fig. 2.
------ PERPLEXUS. Nyst, apud D’Omalius (Sine descript. vel Tab.), Geologie de la Belgique, 1853.[101]