248 BALANID.E. 



22. Balanus eburneus. PL 5, fig. 4 a — 4 d. 



Balanus ebukneus. Aug. Gould (!) Report on the In vertebrata 



of Massachusetts, 1841, fig. G. 



Shell yellowish ivhite. Scutum striated longitudinally : 

 tergum with the spur truncated, the basi-carinal margin 

 generally much hollowed out, and the carina! margin pro- 

 tuberant in the upper part. 



Hub. — United States, from about lat. 42° to Charlestown ; West Indies ; 

 Honduras ; Venezuela ; attached to shells and floatiug wood. Attached to ships' 

 bottoms from Trinidad and Jamaica, associated with B. Untinnabulum, amphi- 

 trite, and improvisus. Brackish water, Salem, Massachusetts, according to 

 Mr. Stimpson. Mus. Aug. Gould, Agassiz, Stutchbury, Cuming, W. Danker, 

 &c. ; very common. 



General Appearance — Shell conical, or almost tubular ; white, with 

 the surface very smooth, covered by thin yellowish epidermis, but with 

 the radii naked. Orifice large, passing from rhomboidal into pentagonal, 

 moderately toothed. Average full size, about one inch in basal diame- 

 ter ; I have seen a specimen 1 *3 in basal diameter, and the same in 

 height. 



Scutum, plainly striated longitudinally : the teeth on the occludent 

 margin small. Internally, the upper surface is roughened : the articular 

 ridge is prominent, and either slightly or not at all reflexed : the pit for 

 the adductor muscle is distinct; the adductor ridge is prominent in a 

 variable degree, and is almost confluent with the articular ridge. In 

 one specimen from Beverly Bay, U. S., the scuta were extraordinarily 

 disintegrated, and I could perceive no trace of the external radiating 

 striae. Tergum, with the basal margin on the carinal side of the spur 

 sometimes deeply (PL 5, fig. 4 b), and sometimes only slightly (fig. 4 d), 

 and rarely hardly at all, hollowed out : when much hollowed out the 

 valve may almost be said to be two-pronged, with the carinal prong 

 narrower than the spur. There is no distinct longitudinal farrow, but 

 the whole scutal margin projects above the general surface of the 

 valve. In the carinal margin, in the upper part, there is a remarkable 

 convexity or protuberance in the same plane with the valve, from 

 which it is separated by a very slight and narrow ridge. The spur is 

 about one fourth of the width of the valve, with its lower end abruptly 

 truncated. Internally, the upper surface is much roughened with 

 finely crenated ridges : the distinct crests for the depressores cover the 

 whole of the so-called carinal prong. 



Compartments ; the radii and alae have their summits oblique, some- 

 times a little rounded, but not smooth. The septa on the sutural 

 edges of the radii are remarkably fine, and closely approximate ; the 



