THE SESSILE BAENACLES. 323 



lar ridge of the scutum is decidedly convex, and the basicarinal lobe 

 of the tergum is less produced. 



CHTHAMALUS SCABROSUS Darwin. 

 Plate 73, figs. 4, 4a. 



1854. Chllutmulus scnbrosus DARWIN, Monograph, p. 4GS, pi. 19, figs. 2a-2d. 



Distribution. Peru to Tierra del Fuego and the Falkland Islands 

 (Darwin). 



The wall is conic, dirty gray when corroded, " dull purplish 

 brown" or pale purplish vinaceous when well preserved; sometimes 

 retaining traces of the cuticle near the base. Eadii usually narrow 

 or scarcely developed; rarely well developed, and then consisting 

 " of small laminae or ridges placed on both sides of the sutures, and 

 interfolded or interlocked together ; usually only a trace of this struc- 

 ture is exhibited." Alfe rather wide, striate. Parietes more or less 

 ribbed. Interior either nearly smooth or roughened, often greenish, 

 the edges of the compartments projecting inward. Diameter about 

 11 mm. 



The scutum is long and narrow. The articular ridge is very promi- 

 nent, forming a lobe in the middle of the tergal margin. This is 

 more conspicuous in the usual worn examples than in the nearly 

 perfect one figured. An oblique ridge, like an adductor ridge, bounds 

 the adductor pit, which is not veiy deep. 



" The terga are very narrow ; they are remarkable in two respects, 

 namely, in the depressor muscle being attached to a plate formed 

 apparently by the union of the usual crests, parallel to the outer 

 lamina of the valve itself, a deep narrow cavity being thus formed; 

 and secondly, in the far more extraordinary circumstance of the 

 existence of a small pit at the extreme basiscutal corner of the 

 valve, in which about half of the scutal lateral depressor muscle is 

 attached." Sometimes this basiscutal pit is very shallow or even 

 entirely wanting, as in the specimen here figured. There is a rounded 

 spur projecting below the basiscutal angle. 



The opercular valves, especially the tergum, are very characteristic. 



Specimens in the United States National Museum from Valparaiso 

 (Cat. No. 48080) are seated upon a rock and are of the conic form, 

 not strongly sculptured. 



According to Darwin : 



This species is the commonest cirripede on the shores of the Falkland. Islands. 

 Many of the specimens are there crowded together, and rendered elongated 



