CHTHAMALUS DENTATUS. 463 



The characters by which this species differs from C. 

 stellatus and from the other species, consist almost exclu- 

 sively in the triangular and equilateral terga, and in the 

 much elongated orifice of the shell ; and these differences 

 I believe to be of specific value. I must, however, confess 

 that I have examined one young specimen attached to a 

 Pollicipes elegans, in which the orifice was not nearly so 

 much elongated, and in which the terga were not so equi- 

 lateral, with the basal margin not quite equably curved, 

 but more protuberant on the scutal than on the carinal 

 side : from an examination, however, of only one specimen, 

 and that a young one, I cannot decide on its specific 

 nature. 



5. Chthamalus dentatus. PI. 18, fig. 3# — 3 c. 



Chthamalus dentatus. Krattss (!) Die Siidafrikauischen Mollusken, 



1848, tab. 6, fig. 27. 



Shell dirty white or brownish : sutures formed by inter- 

 locking teeth : tergum with the carinal margin protuberant, 



Hab. — South Africa, Natal ; West Africa, Loanda and the Gold Coast ; West 

 Indies (?). Attached to ships' bottoms and to littoral shells, and to Tetraclita 

 serrata, Balanus perforatus, and amphitrite ; often attached to Balanus tin- 

 tinnabulum and amphitrite on ships' bottoms. 



General Appearance and Stnicture of Shell. — Shell dirty white, pale 

 brown, or gray: conical, moderately depressed: walls either broadly and 

 irregularly folded (fig. 3 a), with the surface corroded, or (when attached 

 to ships' bottoms and sometimes to other Cirripedes) narrowly and regu- 

 larly folded (3 b), with the surface well preserved, smooth, and generally 

 covered by thin brown membrane. These latter specimens generally 

 have the shell more steeply conical, with the orifice rather smaller, and 

 the radii broader, than in the first-mentioned specimens, which are 

 attached to coast-rocks and shells, and have had their summits worn 

 down. The sutures in all cases are tolerably distinct, and have their 

 edges toothed and interlocked : the crenations are visible before the 

 compartments are disarticulated, when viewed either internally or ex- 

 ternally, but occasionally they are obscure. The radii, when best 

 developed, are rather narrow, and of equal width on both sides of the 

 sutures, with their summits rounded : their surfaces are finely ribbed 

 transversely, each rib corresponding with, or rather forming a point 

 of, the toothed edge. On the under side these teeth usually are a little 



