460 BALANIDJE 



2. Chthamalus antennatus. PI. 18, fig. 2. 



Shell conical, generally smooth ; when not deeply corroded 

 of a jj ale dirty flesh-colour : sutures always distinct: radii, 

 when present, with their sutural edges quite smooth. 



Hab.—New South Wales, (Moreton Bay, 27° S. ; Sydney ; Twofold Bay), 

 Van Diemen's Land (Hobart Town). Attached to littoral rocks and shells; 

 Mus. Brit., Cuming, Darwin. 



General Appearance and Structure of Shell. — Shell conical, rather 

 smooth ; when not much corroded, of a pale dirty flesh-colour ; often 

 covered by membrane; sometimes deeply corroded, extremely rugged, 

 and then of a brown colour ; in this condition not much punctured, 

 as generally is the case with C. stellatus. Sutures almost always quite 

 distinct ; rarely the shell becomes cylindrical with the sutures oblite- 

 rated. Orifice moderately elongated, sub-hexagonal. Radii rather 

 narrow, but not so narrow as in C. stellatus, smooth, with their upper 

 margins very oblique : when disarticulated their edges are quite smooth. 

 The edges of the alae are sometimes crenated, and sometimes not so, 

 being only marked by lines of growth ; they are often rather thick. 

 The parietes are usually rather thick, with their internal surfaces 

 smooth, and not mamillated, as is so often the case with C. stellatus. 

 The largest specimens which I have seen, were '6 of an inch in basal 

 diameter. 



Opercular Valves. — These are hardly distinguishable from those of 

 C. stellatus. The only very slight difference which I can point out is, 

 that the crests for the tergal depressores are less spread out, and depend 

 rather more beneath the basal margin of the valve; and lastly, that the 

 surface of the tergum, just above these crests, is rather prominent. 



Branchice : these are oblong ; taper but little, and have a broad 

 rounded end : they are scarcely plicated. 



Mouth. — The crest of labrum is hairy : the palpi are square, and 

 have no bristles along their basal exterior margins, but long ones at 

 their truncated ends. The mandibles have three or four main teeth ap- 

 parently single: the inferior coarsely pectinated portion is short. The 

 maxillae are deeply notched. 



Cirri. — The first and second pairs, and portions of the third, are 

 darker coloured than the three posterior pairs. The rami in both of 

 the first two pairs are slightly unequal in length. The third cirrus is 

 much longer than the second : in a specimen in which there were six 

 segments in the shorter ramus of the first and second pairs, there were 

 twenty segments in the posterior and shorter ramus of the third cirrus; 

 and in this same individual there were no less thaii forty-nine segments 

 in the anterior ramus. In another specimen (PI. 29, fig. 2) the number 

 of segments in the two rami of the third cirrus, was 20 and 41 ; in 

 another, the numbers were 18 and 53 ; in several other specimens the 



