274 BALANID.E. 



prominent ; in the upper part it is confluent with the articular ridge, 

 nut in young specimens can be seen to be distinct ; in the lower part it 

 borders a large deep cavity for the lateral depressor muscle, in the 

 middle of which there is a very slight longitudinal ridge ; this cavity 

 sometimes is almost closed or arched over in its upper part. In one 

 specimen, the basal margin of the scutum was deeply hollowed out in 

 the middle. The Tergum is remarkably narrow, with its apex produced 

 into a triangular beak, hollow within, and sometimes faintly tinged 

 purple. A deep, closed, longitudinal furrow runs down the valve. The 

 spur is long, remarkably narrow, and pointed. Internally, the spur is 

 produced up the valve as a ridge : the inflected scutal margin, and the 

 prominent articular ridge, are both nearly straight, and parallel to the 

 spur. The crests for the depressores are sharp and very prominent. 



The Parietes are very thick and strong : unlike every other species of 

 the genus, they consist of several very irregular rows, of unequally sized, 

 round or angular tubes (3 b). These tubes or pores are generally short, 

 and are at frequent intervals crossed by transverse septa ; they often 

 rather deserve to be called cells than tubes. New tubes are formed 

 along the inner as well as along the outer lamina. They are lined by 

 dusky purple corium. The internal surface of the parietes is smooth 

 in the upper part, and in the lower, it is reticulated by slight, irre- 

 gularly branching ridges. The carinal internal margin of each com- 

 partment projects a little, as in the case of B. crenatus and balanoides. 

 The lower ed<>;e of the sheath is either hollow beneath, or is united to 

 the walls. The radii in one specimen were broad, with slightly 

 oblique, jagged summits ; generally they are extremely narrow, forming 

 mere ribbons along the lower edges of the compartments, barely ex- 

 tending up as high as the sheath. They can sometimes hardly, 

 or not at all, be seen, until the shell is disarticulated : in rather young 

 specimens the sutural edge is sometimes quite smooth ; in old speci- 

 mens the lower part of the edge has coarse arborescent septa, with the 

 interspaces filled up solidly, whilst the upper part is smooth. The 

 alee are conspicuous from the outside, owing to the little development 

 of the radii ; but owing to the diametric growth not having been great, 

 the part added during such growth is narrow ; the summits of the aloe 

 are only slightly oblique : the sutural edge is coarsely crenated, with 

 the teeth denticulated or slightly arborescent. 



Basis membranous. 



Mouth : labrum with only four very minute teeth : mandibles with 

 four teeth; the third tooth broader than the first ; the fourth small. 

 .Maxillae, with the two upper spines placed, on a slight prominence, 

 beneath which there is a small notch. Cirri of a very dark colour 

 (much injured) : the segments of the first, second, and third pairs very 

 broad and short, protuberant in front, and most thickly clothed with 

 spines ; the third pair is very little longer than the second pair : the 

 sixth pair (in a large specimen above one inch in basal diameter) had 

 the segments broader than long, each furnished with seven pairs of 

 spines. 



Affinities. — This species, though very distinct, evidently comes near 

 to B. balanoides, especially to var. (a). By merely doubling or 



