462 BALANID.E. 



they have the basi-carinal angle of the valve, where the narrow crests 

 for the depressores are placed, pointed and dependent, and the surface 

 of the valve above these crests is prominent. Altogether the opercular 

 valves have a sufficiently distinct character to be recognised without 

 much difficulty. 



Mouth. — The crest of the labrum is not toothed ; the palpi have 

 long hairs along the exterior basal margin. The lower main teeth of 

 the mandibles are plainly laterally double. Cirri. — The pedicel of the 

 second cirrus is extremely broad, and on the exterior margin supports 

 a tuft of very long, finely plumose spines : in some specimens each of 

 the lower segments of the anterior ramus of this cirrus bore one or two 

 very large spines, doubly and extremely coarsely pectinated. In two 

 specimens the rami of the third cirrus were of equal length : but in one 

 specimen (from Iquique, Peru), having seven segments in the shorter 

 ramus of the first and second pairs of cirri, the posterior ramus of the third 

 pair had fourteen segments, and the anterior ramus twenty-two seg- 

 ments. The posterior cirri have segments carrying five pairs of main 

 spines : the dorsal surfaces of the lower segments are serrated. 



4. Chthamalus fissus. PI. 18, fig. 6 a, 6 b. 



Shell broivnish, plicated ; orifice tioice as long as broad : 

 tergum triangular, equilateral, with the basal and carinal 

 margins slightly protuberant. 



Hab. — California, attached to Lottia grandis. Peru (?) ; Mus. Brit. 



General Appearance and Structure of Shell. — Shell globulo-conical, 

 irregular, with the walls much folded. Colour brownish. Sutures 

 generally distinct in young specimens, and nearly obliterated in full- 

 grown individuals. Radii, when present, very narrow. The orifice of 

 the shell, in full-grown specimens which have their summits a little 

 worn, is narrow, much elongated, about twice as long as wide, oval or 

 ovate, with the rostral end the narrowest : the elongation of the orifice 

 offers almost the only character by which this species can be externally 

 recognised. The lateral compartments are rather wider than usual in 

 proportion to the rostro-lateral compartments. Basal diameter of largest 

 specimen '2 of an inch. 



Scuta, elongated transversely, with the pit for the adductor muscle 

 bordered on the under side by an adductor ridge rather more prominent 

 than usual in this genus. Terga, triangular, equilateral, w T ith the mar- 

 gins slightly curved and protuberant : the basal margin is regularly 

 and equably curved from one end to the other. 



Neither the Mouth nor Cirri offer any peculiar characters distinct from 

 the genus. I may mention, however, that the crest of the labrum is 

 toothed, and that the segments of the posterior pairs of cirri support 

 five pairs of main spines. 



