CHTHAMALUS SCABROSUS. 469 



specimens from the Falkland Islands, both edges of each suture were 

 inflected, forming a double ridge, with roughened edges, resting on the 

 basal membrane, and supporting the shell. I must mention that in 

 my notes made at these Islands, I remark that the basal membrane 

 seemed sometimes to be surrounded by a calcareous rim ; none of the 

 specimens brought home are thus characterised ; but bearing in mind 

 the affinity of this species to C. intertextus, no doubt we have here 

 an indication of the shelly ledge surrounding the basis, as described 

 under that species. The largest specimens which I have seen are a 

 quarter of an inch in basal diameter. 



The Opercular Valves generally have their summits much worn down. 

 The scuta are elongated in the line of the longer axis of the orifice ; the 

 articular ridge is very prominent, and is placed in the middle of 

 the tergal margin. The terga are very narrow, as in some varieties of 

 C. stel/atus: they are remarkable in two respects, namely, in the de- 

 pressor 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 (fig. 2d, p) being thus formed ; and secondly, in the 

 far more extraordinary circumstance of the existence of a small pit (q) at 

 the extreme basi-scutal corner of the valve, in which about half of the 

 scutal lateral depressor muscle is attached : I have observed no other 

 instance in any cirripede of the partial attachment of a muscle pro- 

 perly belonging to one valve to another valve. The figures of the 

 valves 2b, 2 c, 2 d> are from specimens most unusually perfect, with 

 the upper portion not worn away ; the ordinary appearance of the valves 

 as seen from above, is given in fig. 2 a; at fig. 2d, a view is given of the 

 tergum seen from vertically beneath, showing the cavity for its own 

 depressor muscle, and for part of the lateral depressor muscle of the 

 scutum. 



Mouth. — The crest of the labrum is hairy, without teeth : the palpi 

 have long spines at the end, but none along the inferior margin : the 

 mandibles have either four or five graduated teeth, the lower ones of 

 which are plainly double laterally : the maxillae have a very sinuous 

 edge. Cirri: the first and second pairs are very short : on the four 

 posterior pairs the segments support either four or five pairs of main 

 spines, with the small intermediate spines rather larger than usual. 



Branchiae. — None ; but where they ought to occur, there are two very 

 slight ridges clothed with hairs, about the -j--j^th of an inch in length. 

 On the prosoma, there is a slight ridge, extending from the base of 

 the first cirrus towards the adductor scutorum muscle, also clothed 

 with hairs; this unusual character of the prosoma being hairy is 

 common to C. dentatus. 



This species is the commonest cirripede on the shores of 

 the Falkland Islands : many of the specimens are there 

 crowded together, and rendered elongated and cylindrical, 

 with the walls very thin, and the sutures often obliterated ; 

 as the opercular membrane is very narrow, the opercular 

 valves are much influenced both in their outline and in their 



