BALANUS. 13 



Scutum and tergum articulated together, sub-triangular ; compartments six ; basis 

 calcareous or membranous. 



The genus Balanus already includes 45 species, recent and fossil, and consequently 

 in my volume published by the Ray Society, I have divided the genus into sections, 

 on characters derived from the porosity of the parietes, radii, and basis ; and on whether 

 the basis be membranous or calcareous. But as here we have to describe or notice only 

 eleven species, I have thought it more convenient to drop the sections, and in their place 

 add a few words to each of the diagnostic characters. The genus is quite distinct from 

 all the other genera of Sessile Cirripedes, with the exception of the sub-genus Acasta, 

 from which its separation, it must be confessed, is in one sense artificial ; for the 

 species of this sub-genus graduate into those of Balanus (such as B. calceolus and its allies), 

 which have their shells elongated in the rostro-carinal axis, and which live attached to 

 Gorgonise. These latter species have been generically separated by some authors from 

 true Balanus ; but I have found it impossible to effect this ; and even the section of the 

 genus, including these species, is hardly distinct enough from the adjoining sections. 

 On the other hand, the sub-genus Acasta, in another sense, is a very natural one, inas- 

 much as all its species are closely allied together in essential structure, in general 

 appearance, and in habit ; and as the genus Balanus is already large, I have thought 

 it best t A adopt Acasta, which has been already admitted by many authors as a sub-genus. 

 I need only further remark, that from reasons already assigned, I have thought it useless 

 to give in this work long generic descriptions. 



1. Balanus tintinnabulum. Tab. T, fig. \a — Id. 



Lepas tintinnabulum. Linn. Syst. Naturae, 1/67. 



— — Ellis. Phil. Transact , vol. 50, 1758, Tab. 34, figs. 8 and 9. 



— — Chemnitz. Neues. Syst. Conch., 8 B. (1785), Tab. 97, 



figs. 828-831. 

 Balanus TULIPa. Bruguiere. Encyclop. Meth., 1789; sed non B. tulipa alba, m 

 Chemnitz ; nee non B. tulipa, 0. F. Miiller, Zoolog. Dan. ; nee 

 non B. tulipa, Poli, Test, ut Sicilise. 

 — — G. B. Sowerby. Genera of Recent and Fossil Shells, Tab. Genus 



Balanus. 

 Lepas crispata (var.) Schr'oter. Einleitung Conch., vol. iii, Tab. 9, fig. 21. 



— spinosa (var.) Gmelin. Linn. Syst. Nat. 



— tintinnabulum, spinosa, cbispata et porcata. W. Wood. General Con- 



chology, 1815, PL 6, figs. 1, 2. PL 7, figs. 4, 5. PI. 8, figs. 1—5. 

 Balanus tintinnabulum. Chenu. Illust. Conch. 



— d'Orbignii (var.) Chenu. Illust. Conch., Tab. 6, fig. 10, sed nqn Tab. 4, 



fig. 13. 



— crassus. Sowerby (!) Min. Conch., 1818, Tab. 84. 



