20 ORDER I. SESSILES. 



BALANUS, Bruguiere. 



Testa conica vel elongato-conica, valvis sex imequalibus lateraliter ferru- 

 minatis composita ; apice pervio, basi vel planulata vel concava 

 lamella testacea clausa. Operculum internum, valvis quatuor mo- 

 bilibus compositum. 



The genus Balanus includes by far the most numerous of the Sessile 

 Lepades ; their shells are exceedingly variable in form, growing irregu- 

 larly to any kind of substance they come in contact with, and from 

 which their animals have not the power of displacing them. For this rea- 

 son we readily adopt the arrangement of Sowerby and De Blainville, in 

 reuniting to this genus the Acastoe of Dr. Leach ; they were separated on 

 account of the base of the shell assuming a concave or cup-shaped form ; 

 but this merely arises from the peculiarity of their place of habitation, 

 which is generally in soft sponges. 



The shell of Balanus may be described as being conical or elongately 

 conical, composed of six unequal pieces or valves, closed at the sides 

 upon a firm testaceous base, which is either flat or concave, according to 

 its place of habitation. The shell is open at the top, with an operculum 

 inserted, consisting of four moveable valves. 



The Balani are abundantly prolific, growing in large irregular clusters 

 one upon the other. 



Examples. 



PI. VII. Fig. 1. 



Balanus tulipa, Lamarck, Anim. sans vert., new edit., vol. v. p. 658. 

 Balanus tintinnabulum, var. Sowerby. 

 Lepas tulipa, Poli. 



PI. VII. Fig. 2. 



Balanus spinosus, Lamarck, Anim. sans vert., new edit., vol. v. p. 661. 



Enc. Me'th., pi. 164. f. 10. 

 Lepas spinosa, Gmelin. 



