THE SESSILE BAKNACLES. 261 



The barnacle is thin, the compartments rather easily separated. 

 They are sometimes more or less roughened, but not ribbed or plicate. 

 The thin basal edge is not crenulated, but there are sometimes some 

 fine vertical striae within the edge. " The scuta are remarkable for 

 not having any adductor ridge or crests for the depressor muscles." 



There is a cylindrical specimen in the United States National 

 Museum from the Isaac Lea collection, without locality. 



ELMINIUS PLICATUS Gray. 



1854. Elm Inins plicalus Gray, DARWIN, Monograph, p. 851, pi. 12, figs. 

 2-2/. 



Distribution. New Zealand. Two specimens without opercular 

 valves. Also two from " Orange Bay," with Tetraclita rosea; no col- 

 lector given, and locality doubtless erroneous. 



Two other species of Ehninius have been described from New 

 Zealand, E. xinuatus and E. rugosus Hutton, 1 and two from Aus- 

 tralia, E. simplex and E. modestus Darwin. Professor Grtivel has 

 described a very small form from the breakwater at Ponta Delgada, 

 San Miguel, Azores, as E. cristaUinus. This is the only species known 

 in the Northern Hemisphere. 



Genus CREUSIA Leach. 

 1854. Creiisia Leach, DARWIN, Monograph, p. 375. 

 Darwin describes this genus as consisting of- 



Coinpartments four, furnished with radii ; basis cup-forrned ; attached to 

 corals. 



This genus is represented in the United States National Museum 

 by five small specimens on a bit of coral, I. Lea collection. No locality 

 is recorded. 



Darwin records the single species recognized by him, Greusia 

 spinulosa Leach, from both the West and East Indies. No definite 

 West Indian locality is given. 



Genus PYRGOMA Leach. 



1854. Pyrgoma Leach, DARWIN, Monograph, p. 354 (see for synonymy, etc.). 

 1838. Duplocona SCHLUTER, Kurzgefasstes systematisches Verzeichuiss 



meiner Conchyliensaruinlung, p. 38, for D. UevigaM Schliiter ( =Balanus 



tl uploconus Lamarck ) . 



According to Darwin, this genus possesses a "shell formed of a 

 single piece; basis cup-formed or subcylindrical, attached to corals." 



Pyrgoma is considered a further development of Creusia, in which 

 the four compartments have become wholly concrescent. 



i Trans. N. Z. Inst., vol. 11, 1879, p. 328. 

 4729 Bull. 9316 18 



