THE SESSILE BAENACLES. 261 



The btirnacle is thin, the conipartinents rather easily separated. 

 Thej^ 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 stritie 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, ^vithout locality. 



ELMINIUS PLICATUS Gray. 



1854. Ehninius pUcutiiN Gray, Daiuvin, IMonograph, p. 351, pi. 12, figs. 

 2a-2f. 



Distribution. — New Zealand. Two specimens without opercular 

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

 lector given, and locality doubtless erroneous. 



Two other species of Ehninius have been described from New 

 Zealand, E. siniiatus and E. rugosus Hutton,^ and two from Aus- 

 tralia, E. simplex and E. Ttiodestus Darwin. Professor Gruvel has 

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

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

 in the Northern Hemisphere. 



Genus CREUSIA Leach. 



1854. Crev.sia Leach, Darwin, IMonogruph, p. 375. 



Darwin describes this genus as consisting of — 



Compartments four, furnished with radii; basis cup-formed; 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, Creusia 

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

 West Indian locality is given. 



Genus PYRGOMA Leach. 



1854. Pyrgoma Leach, Darwin, IMonograph, p. 354 (see for synonymy, etc.). 

 1838. Dvplocona ScHLiJTEK, Kurzgefasstes systematisches Verzeiclmiss 



meinor Conchyliensammlung, p. 38, for D. Iwvigata Schlilter (=Balanus 



(Iiiploconus 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 >vhich 

 the four compartments have become wholly concrescent. 



1 Trans. N. Z. lust., vol. 11, 1879, p. 328, 

 4729°— Bull. 93—16 18 



