234 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The tergum is triangular, much wider than the scutum-. It is flat 

 externally and sculptured like the scutum. Articular ridge is very 

 short and acute; articular furrow wide. The spur is extremely 

 short, two-thirds as wide as the basal margin, extremely close to 

 and curving into the basiscutal angle. The whole inner face is 

 roughened with lengthened tubercles. There are no crests for the 

 depressor muscle. 



Compartments. The carinolateral compartment is about half as 

 wide as the lateral. There are no radii, merely a slight thickening 

 along the radial edges. The alse are wide, with thin, oblique sum- 

 mits. The sheath is about two-thirds the length of the carina and 

 lateral compartments, over one-third the length of the rostrum. 

 It bears many fine horizontal ridges closely set with short, golden 

 bristles. The parietes are not hollowed out below the sheath and 

 are distinctly ridged longitudinally. The basal edges of the com- 

 partments are blunt and nearly smooth. The lower part of the 

 rostrum tapers to a rounded extremity (appearing more obtuse in 

 the foreshortened figure 25). 



None of the dry specimens examined contained the body and 

 limbs. 



This species is know y n by numerous specimens, more or less per- 

 fect, collected by Mr. Orcutt in 1889. It is twice the size of the 

 largest specimens of B. (led iris Darwin and differs from that West 

 Indian species in the following respects: The radii are practically 

 absent. The sheath is much longer. The interior is much more 

 strongly ribbed. The scutum is constantly much narrower relative 

 to its length. Its articular ridge is shorter, and there is a u^ ell- 

 developed adductor ridge. The tergum is much wider, with a 

 wider, shorter spur, and roughened interior. 



The external sculpture of the parietes is essentially similar in 

 the two species, but the minute wrinkling is more fully developed 

 in B. orcutti. The type-specimen is figured. 



Fragments of a small, delicate species of Membrano7)alanus were 

 found in a sponge from Cape St. Lucas, Lower California. The 

 rostrum is much narrower than that of B. orcutil; Cat. No. 32933 

 U.S.N.M. 







Subgenus CONOPEA Say. 



1822. Conopea SAY, Journal of the Academy of Natural Sciences of Phila- 

 delphia, vol. 2, p. 323. 



1825. Conoplea GRAY, Annnls of Philosophy, new ser., vol. 10, pp. 98, 103. 



1839. Balaninus O. G. COSTA, Corrispondenza Zoologica, vol. 1, p. 181 ; Fauna 

 del Regno di Napoli, MolHichi, Cirropecli, p. 19, monotype B. galeatus. 



1854. Bahmiis, Section B, DARWIN, Monograph, p. 216. 



1913. PateUa-Balanus HOEK, /S%o#a-Expeditie, Monographic 316, Cirripedia 

 sessilia, pp. 160, 162, 221 (Type Balanus calceolus Ellis, Darwin). 



