278 BALANID^l. 



mollusca, stems of fuci, and stones; often associated with B. porcatus and 

 crenatus. 



Fossil. — In glacial deposits at Uddevalla in Sweden, and Beaufort in Ca- 

 nada ; Mus. Lyell. Banks of the Dwina, Russia ; Mus. Murchison. Greenland, 

 " in blue clay," according to Spengler. 



General Appearance. — Shell tubulo-conical, very smooth, white, ge- 

 nerally 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 quar- 

 ters 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, arti- 

 cular 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. Alee 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 fur- 

 rowed in lines radiating from the centre. 



Mouth : labrum with scarcely perceptible minute bead-like teeth thinly 

 scattered along the edge. Palpi and outer maxillce 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. Maxillce 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 



