AFFINITIES. 153 



the Chthamalinae ; and on the other hand, Pachylasma, a 

 member of the Chthamalinse, has a shell, which if not 

 examined during its earliest growth, would be placed with- 

 out doubt amongst the Balaninae. But it fortunately so 

 happens, that in no one character of the body does Pachy- 

 lasma approach the Balaninae more nearly, than do the 

 other members of its sub-family; or Chelonobia approach, 

 in the same respects, the Chthamalinae. It is only in 

 Chthamalus, of which the shell clearly places it in the sub- 

 family bearing its name, that in some of the species, the 

 less bullate lab rum, — the larger palpi, — the lower teeth 

 of the mandibles being laterally double, — and the lower 

 segments of the third pair of cirri being thickly clothed, 

 like the lower segments of the second pair, with bristles — 

 all show that these species make an approach in structure 

 to the Balaninae. 



It will be seen that I have divided the Balaninae into two 

 little groups, according as whether the branchiae consist of 

 one or of two plicated folds of membrane, and as whether 

 or not the scutum and tergum are articulated together. 

 I have been greatly tempted to follow Drs. Leach and 

 Gray, who have separated the second of these groups, con- 

 taining the genera Coronula, Tubicinella, Xenobalanus, and 

 Platylepas, into the sub-family of the Coronulinae. Cer- 

 tainly these genera have a peculiar aspect in common, and 

 agree in being parasitic and imbedded in the skin of Ceta- 

 ceans, as is the case with the first three genera, or in that of 

 turtles, manatee, and sea-snakes, as in Platylepas. Though 

 these genera possess several peculiar characters, yet I can 

 find none common to all four, excepting their imbedment in 

 the skin of Vertebrata, their double branchiae, and their 

 non- articulated opercular valves; and these I do not think 

 of sufficient importance to serve for the separation of a sub- 

 family ; for in Chthamalus, one species has double branchiae, 

 one species has no branchiae at all, and the other species have 

 single branchiae ; so again in Chelonobia, the scutum having 

 only a horny articular ridge, makes an approach to Coronula 

 and its allies. I may further specify that the folded walls, 

 a singular character common to Coronula, Platylepas and 

 Xenobalanus, fails in Tubicinella; the open tubes and the 



