184 BALAMDiE. 



others, with the exception of the uppermost pair. The 

 outer maxilla are, on their inner faces, obscurely divided 

 into two lobes. 



Cirri — The rami of the first pair are unequal, the 

 shorter one sometimes not being more than half the length 

 of the other ramus : the segments of the shorter ramus are 

 broad, and are, together with the lower segments of the 

 longer ramus, thickly clothed with spines ; in some species, 

 as in B. perforatus, the anterior surfaces of the segments, 

 more especially of the shorter ramus, and of both rami of 

 the second pair are produced (PI. 29, fig. 4), so as some- 

 times to form very remarkable projections. The segments 

 of the second and third pairs are always thickly clothed 

 with spines, as also are their pedicels. The third pair is 

 rather longer than the second ; but in B. vestitus and 

 imperator it is much longer, and is otherwise somewhat 

 different. The dorsal and basal margin of the pedicel of the 

 third pair, in some of the species, as in B. tintinnabulum , 

 is produced backwards on the thorax, and forms a mem- 

 branous plate fringed with fine spines. The three posterior 

 and longer pairs of cirri have from three to rarely eight or 

 ten pairs of long spines on each segment, with generally 

 one or two minute spines in the middle between each pair : 

 their pedicels have a regular double row of spines. 



The penis is long and hairy: in most of the species there 

 is, at its dorsal basis, a small, sharp, flattened, imperforate 

 projection ; first observed by Poli : but this is sometimes 

 absent, as in B. crenatus, though present in the closely 

 allied B. balanoides ; and its presence is variable in B. tin- 

 tinnabulum. All the species have large plicated branchiae. 

 The base of the sack in several species is furnished with 

 inwardly projecting Alimentary appendages. In B. perfo- 

 ratus, crenatus, and i?nprovisus, and I believe in other species, 

 the upper part of the stomach is furnished with a circle of 

 branching caeca. 



On the variation of the species ; their arrangement and 

 affinities; value of the characters used; changes during 

 growth. — Owing to the great variation in external characters, 

 to which almost all the species are subject, and likewise to 



