THE SESSILE BARNACLES. 315 



Tlie crests for the depressor muscles are short but project well over 

 the basal margin. 



The mandible has three large teeth and a pectinated lower point 

 (fig. 92r). The maxilla has spines in the usual three groups; those 

 of the lower group are very fine and close (fig. 92?;). 



Cirrus i has unequal rami with 8 and G segments, the posterior 

 ramus slightly over half as long as the anterior. 



Cirrus ii has rami of 10 segments, the anterior ramus about two 

 segments longer than the posterior. Posterior ramus is much more 

 slender than the anterior; about half as wide. A few spines in the 

 terminal segment of the anterior ramus are lanceolate with minutely 

 serrate edges, somewhat as figured for typical C. stellatus, but more 

 slender. 



The remaining cirri have subequal rami, the segments bearing four 

 pairs of spines. I note a minute fifth pair on a few segments. 



The caudal appendages are about three-fourths as long as the cirri, 

 slender, each composed of 21 segments bearing some delicate spines. 

 They are closety similar (fig. 9 % 2a). 



The special features of this species are in the appendages. The 

 rami of the first cirri are more unequal in. length than usual; the 

 second are unequal in width, and there are long caudal appendages. 

 The form of mandible is common to several other species. 



Before dissecting C. caudatus I thought it a form of C. dentatus 

 Krauss, which I know only from the published accounts. The hard 

 parts agree in the main with that species, as described by Darwin, 

 but several minor differences may be noted. The parietes are not 

 ribbed, though there is a trace of such sculpture near the bases of 

 some compartments. 



The crests of the tergum project more over the basal margin. In 

 C. dentatus, according to Darwin, the " tips of the second pair of 

 cirri have many coarsely pectinated spines," and there are but six 

 segments in the shorter ramus. Both of these characters differ from 

 C. caudafus. The mandible of C. dentatus has not been figured, but 

 it appears from the description to be like that of caudatus. The 

 chief difference is in the long and well-developed caudal appendages 

 of C. caudatus. Darwin had an abundance of material of C. dentatus, 

 and. it does not seem likely that structures so conspicuous and remark- 

 able could have escaped his acute observation, if they were present 

 in that species. 



C. caudatus is the only species of Chthamalus in which caudal 

 appendages have been seen. I could find no trace of them whatever 

 in C. hcmbeli and C. withersi, which have the same form of mandible 

 as C. caudatus. 



