Hab.—Coast of Yorkshire; Scotland; Galway, Ireland; Isle of Man, and Anglesey, twelve fathoms. Generally in deep water; not very common. George’s Bank, Massachussetts, United States; Mus. Aug. Gould. Iceland, Finmark, and the Faroe Island, according to Spengler. Attached to crustacea, mollusca, stems of fuci, and stones; often associated with [B. porcatus] and [crenatus].
Fossil.—In glacial deposits at Uddevalla in Sweden, and Beaufort in Canada; Mus. Lyell. Banks of the Dwina, Russia; Mus. Murchison. Greenland, “in blue clay,” according to Spengler. Red Crag (Sutton) Mus. S. Wood.
General appearance.—Shell tubulo-conical, very smooth, white, generally more or less covered by yellow thin membrane: orifice large, sub-triangular: radii moderately broad, with their more or less oblique summits slightly rounded and smooth; from this circumstance the shell has been justly compared to the half-opened flower of a white tulip. Specimens often exceed an inch in basal diameter; I have seen one from Scarborough two inches in diameter and one and three quarters in height: another specimen was 1.6 in diameter and 3 in height. The specimens in the glacial deposits seem even to have acquired larger dimensions, one from Uddevalla being nearly four inches in height.
Scuta, elongated, flat, feebly striated longitudinally: internally, articular ridge short, moderately prominent: adductor ridge, confluent in the upper part with the articular ridge, running straight down and forming a rather large cavity for the lateral depressor. Terga feebly striated longitudinally, with a longitudinal furrow, having the sides, in old specimens, partly closed in: the basal margin slopes much towards the spur, which is rather long and narrow, with its end rounded: it is placed at about its own width from the basi-scutal angle. Internally, articular furrow narrow; crests for the depressores moderately prominent, but in a variable degree.
Compartments: these are unusually thin, and separate easily: the parietes are finely ribbed longitudinally on their insides; the bases of these ribs being just perceptibly denticulated. Radii, with their summits oblique (usually at about an angle of 45°), slightly arched and quite smooth: the smoothness is produced by the edge being a little inflected: sutural edge quite smooth, without even a trace of septa or denticuli. Alæ oblique, generally rather less oblique than the summits of the radii: sutural edges smooth, with an excessively fine linear furrow running along the edge, a little towards the inner side, and filled with a yellow ligamentous substance: a furrow of this kind I have seen in no other species.
Basis, solid, not permeated by pores; either smooth, or slightly furrowed in lines radiating from the centre.
Mouth: labrum with scarcely perceptible minute bead-like teeth thinly scattered along the edge. Palpi and outer maxillæ rather sparingly clothed with hairs. Mandibles with teeth rather sharp; the fourth and fifth teeth small, but well developed; inferior angle pointed with fine spines. Maxillæ with a deep notch under the two upper great spines. Cirri, the first pair is short, with rami of nearly equal length: the segments are not protuberant in front either in the first or second pairs. In the posterior cirri, the segments bear four pairs of spines, with a tuft of rather long intermediate spines: in young specimens there are only three pairs: the spines in the dorsal tufts are short and thin.
When the shell is disarticulated, this species cannot be confounded with any other; but judging by external characters alone, it may sometimes be very easily confounded with [B. eburneus], and I have received the two species under this one name from Massachussetts: generally [B. Hameri] may be distinguished from [B. eburneus] by the smoothness of the summits of its radii, and by the so-called epidermis being of a darker yellow.
With respect to the fossil specimens from the glacial deposits, I have little to add; I have seen one from Uddevalla, as already remarked, four inches in height, and a lateral compartment broader by one fourth than the same compartment in any recent specimen. As Sir C. Lyell remarks (Phil. Transact.), the compartments are always found separated, which is accounted for by their weak union in a recent state. This species, when fossil, is usually associated with its deep-water congeners [B. porcatus] and [crenatus], as at the present day.
I must here mention that I have examined a considerable number of separated compartments, without opercular valves, brought from Barbados, in the West Indies, showing the existence there of a closely allied or possibly identical species. The only difference which I can point out in these compartments is, that the parietes are rather thicker, and the radii rather narrower, with more oblique summits: some of the compartments are two inches in length. It seems very improbable that the true [B. Hameri] should extend to the West Indies, but after what has been seen in the case of [B. crenatus], this is possible.