194 BALANIDJE. 



[D] 



Parietes permeated by pores. Basis and radii not per- 

 meated by pores. 



Basis membranous. 



M 



Parietes and radii not permeated by pores. Basis some- 

 times permeated by pores, sometimes not, sometimes exces- 

 sively thin and hardly distinguishable * 



Section a. 



1. Balanus tintinnabulum. PL 1, fig. a — /: PI. 2, 

 fig. 1 a — 1 o. 



Lepas tintinnabulum. Linn. Syst. Naturae, 1767. 



— — Ellis. Phil. Transact., vol. 50 3 1758, 



Tab. 34, figs. 8 and 9. 



* The following species might, owing to variation, or to the obscurity of their 

 structure, without care, be classed in the wrong sections : — In A, Balanus 

 Ajax, from living attached to Milleporae, is sometimes elongated in its rostro- 

 carinal axis, and from having its radii only finely porose, it might be classed 

 in B : on the other hand, Bal. stultus is sometimes but little elongated, and the 

 basis hardly boat-formed, and hence might be classed in A. The distinction 

 between all the species in (B) and the sub-genus Acasta is artificial. 



In sections C and D, I have seen one specimen of B. spongicola with a solid 

 basis, and very young specimens of B. improvisus are thus characterised, and 

 therefore these species are liable to be placed in the wrong section, D: Bal. 

 nubilus, also, has part of its base non-porose, and therefore likewise might be 

 placed in D : on the other hand, the circumference of the basis in B. patellaris 

 is often porose, and hence this species, which belongs to D, might be placed 

 inC. 



In Bal. glandula, in D, the parietes of the compartments, without several 

 were examined, might be thought to be solid, and therefore this species might 

 be wrongly placed in F ; on the other hand, the fossil B. unguiformis, in F, 

 often has porose parietes, and such specimens would naturally be placed in D. 

 Lastly, without care, B. flosculus might be thought to have a membranous 

 basis, and so get placed in E. 



The genus Pachylasma, without an examination of the animal's body, might 

 easily get misplaced in the wrong genus, amongst the species in the last section 

 (F) of Balanus, yet there can be no doubt that Pachylasma belongs to the 

 Chthamalinae. 



