266 BALANID^E. 



broad, with its lower end truncated and rounded ; internally, articular 

 ridge very prominent; crests for the depressores well developed. 



Compartments .- — The internal surface of the parietes is smooth in 

 the upper part beneath the sheath, but generally very strongly ribbed 

 in the lower part, the ribs being plainly denticulated at their bases ; in 

 other specimens, the ribs are very small, and even in parts quite 

 obsolete. The parietal pores are short and imperfect, sometimes reduced 

 to an extremely minute size, to be detected only when the walls are 

 broken across near the basal edge, and most carefully examined ; occa- 

 sionally not even a trace of a pore exists. Hence in this respect, 

 this species offers a singular case of variation. The radii are narrow, 

 and of nearly the same width from top to bottom ; their very oblique 

 summits, when well preserved, are smooth and rounded ; their sutural 

 edges are ribbed or crenated with extremely fine, smooth septa ; the 

 recipient furrow is plainly marked by these septa. The sutural edges 

 of the alae are crenated ; their summits are less oblique than those of 

 the radii. 



Basis, thin, finely furrowed in lines radiating from the centre ; 

 margin sometimes deeply sinuous. 



Mouth : labrum with the central notch rather widely open, with four 

 teeth on each side of it : palpi with very short spines along their inner 

 margins : mandibles with the fourth and fifth teeth forming mere knobs : 

 maxillae small, with a mere trace of a notch under the two great upper 

 spines. Cirri ; first pair with the rami unequal by three or four seg- 

 ments, the longer ramus being only one quarter of its own length 

 longer than the other ramus. Second pair short, with the segments 

 (and those of the shorter ramus of first pair) somewhat protuberant. 

 Third pair with the rami one third longer than those of the second 

 pair. Sixth pair with the upper segments elongated, and bearing six 

 or seven pairs of spines. 



Affinities. — This species in general appearance closely approaches 

 B. crenatus and balanoides, and it is related to them in many essential 

 parts, such as in the opercular valves. It agrees with B. halanoides, 

 and differs from B. crenatus, in the smallness and imperfection of the 

 parietal pores, and in the radii having rounded summits ; it agrees 

 with B. crenatus in the structure of its basis, and in the prominent 

 longitudinal ribs on the internal surface of the parietes, and differs 

 from that species in the spur of the tergum being squarer, and in the 

 scutum having an adductor ridge. 



Range. — From the appearance of the Californian specimens, I suspect 

 that they had adhered to tidal shells and to wood. The specimens in the 

 British Museum, adhering to Pollicipes polymerus, consist of two lots, 

 one of unknow r n origin, and the other certainly brought from the 

 southern half of the Pacific Ocean by Sir James Ross : it deserves 

 notice, that the Pollicipes polymerus, the supporting object, ranges 

 from California to the southern Pacific Ocean. 



