THE SESSILE BABNACLES. 229 



^ BALANUS QUADRIVITTATUS Darwin. 



1854. Balanus quailrivittatus Darwin, IMonograph, p. 284, pi. S, fig. 1. 

 1D13. BalaiiHS quadrivittfilus Darwin, Hoek, iS'i^oi/a-Expeditie, Cirripedia, 

 Monograpliie 31b, p. 213, pi. 21, figs. 15-20; pi. 22, figs. 1, 2. 



Type. — British Museum, East Indies or Philippines. 



Distribution. — Philippines and Malay Archipelago. Taken by the 

 Albatross at Catbalogan, Samar, gro^Ying, associated with small B. 

 amarijUis, on a living Euchclus found on the reef. 



Subgenus MEMBRANOBALANUS Hoek. 



Mcmhrano-Balanus Hokk, The Cirripedia of the Siboga-Expeditioii, Siboga- 

 Expeditie, Monograpliie olb, pp. 159, 205, May, 1913. 



Walls thin, impervious, the compartments weakly united; sutural 

 edges of the radii not septate; basis membranous; rostrum boat- 

 shaped, about twice as long as the other compartments; spur of the 

 tergum very short and broad. First cirri with very unequal rami. 

 Fourth cirri having teeth on part of the segments. Sixth cirri com- 

 posj?d of long segments bearing few pairs of spines (4 in known 

 species) . Living embedded in sponges. 



Type. — Balanus declivis Darwin. 



This group, as proposed by Hoek, " corresponds to Darwin's 

 Section E and contains the species with a membranous basis." As 

 the only species mentioned are B. longirostruni.^ new species, and 

 B. declivis Darwin, the latter being a member of Darwin's Section 

 E, I restrict the new section to this aberrant group, selecting B. 

 declivis as its type. The poreless walls and armed cirri of these 

 forms show^ that they are not directly related to other species having 

 the basis membranous, and I believe that the two series should be 

 widely separated in a natural classification. Membranobalanus is 

 related to Amvatohalanus and to Acasta. 



KEY TO SPECIES OF MEMBRANOBALANUS. 



a\ Small, fragile, rostrum less than 10 mm. long ; radii present ; tergum about 

 as wide as scutum, the spur occupying half the basal margin; scutum 

 with the adductor ridge very weak or wanting. 



6\ Rostrum convex throughout. Its lower half broadly rounded. Fourth 

 cirri with the segments of outer ramus armed with erect distal 

 teeth and with large, recurved teeth on the anterior protuberance. 



West Indies B. declivis Darwin 



h\ Rostrum grooved by a median longitudinal furrow; its lower half 

 narrower, tapering; scutum with two shallow longitudinal depres- 

 sions externally. Fourth cirri armed with erect teeth near the 

 distal margin of the lower 10 segments. East Indies. 



B. longirostrum Hoek * 



1 Balanus longiro'strum Hoek, Cinipedia of the iS/6ojo-ExpecIitie, Monographie 316, p. 205, pi. 20, figs. 

 S-16, 1913. Off Dongola, Palos Bay, Celebes, 3G meters, and east of Dangar Besar, Saleh Bay, 36 meters. 

 This species is not represented in the collection of the United States National Museum. It seems to be 

 closely related to B. (iec/ij)/s, but is clearly a distinct species by reason of the marked diiference in the 

 armature of the fourth cirri, the protuberant segments of the shorter ramus of tlie fust cirri, and various 

 minor details of structure. An undetermined form similar to B. declivis has been reported from the Black 

 Sea by Czerniavski. See Zoological Record, 1S70, p. 205. 

 4729°— Bull. 93—16 16 



