182 



BULLETIN 93^ UNITED STATES NATIONAL MUSEUM, 



SEMIBALANTJS, new subgenus. 



T/ie hasis is membranous,- parietes porous, or with the pores filled 

 up; hiterio}' not long Hud inalhj rihhed., but usually having small 

 anastomosing wrinkles near the basal edge; rostrum not prolonged 

 downward below the other compartments. No spinules or "teeth" 

 on the cirri. 



Type. — Balanus carlosus. 



I do not regard B. hcdanoides and B. glandula as transitional be- 

 tween the Balani with solid and those with porous walls. The}^ 

 are porous forms which have filled up the pores more or less com- 

 pletely, in some individuals. Wliile related to the typical group of 

 Balanus, this subgenus is strongly individualized. The membran- 

 ous basis and the profusely bristly third cirri, without spinules on 

 the outer faces of the segments, are primitive characters, but the 

 closing of the parietal pores in B. halanoides and their multiplica- 

 tion in B. carlosus are relatively more evolved features than the 

 ordinary types of porous wall. 



KEY TO Sl'KCIES. 



Parietes copiously ribbed externally with several rows of unequal pores ; tergum 

 very narrow, with long, narrow spur and a more or less closed external 

 furrow B. carlosus. 



Parietes coarsely folded or smooth, the pores normal or obsolete ; tergum with 

 short spur and no trace of an external furrow B. halanoides. 



BALANUS HALANOIDES (Linnasus). 

 Plate 44. 



1766. Lcpas halanoides Linn^us, Systema Naturre, ed. 12, p. IIOS. 

 1789. Balanus flstulosus BEUGUifiEE, Encyclopedie Methodique, p. 166. 

 1700. fLcpas elongata Gmelin, Syst. Nat., ed. 13, p. 3213. 

 1799. Balanus clavatus Pulteney, Catalogue of the birds, shells, and 



some of the more rare plants of Dorsetshire, p. 2.5. 

 1818. Balanus palinulatus Lamabck, Auim. sans Vert., vol. 5, p. 394. 



