322 



BULLETIN 9:], UNITED STATES NATIONAL MUSEUM. 



pressor muscle pit is general!}^ but not always crossed by short 

 crests, as in several other West Coast species. 



The tergnni is concave within. 'The spur fro'jeets in a hlunt point 

 helow the ha-siscutal angle. There is a narroAV, basicarinal lobe, 

 with a few short crests for the lateral depressor muscle. 



The labrum is concave in the middle, and has many long hairs 

 at the sides. 



The mandibles and maxillse (fig. 9G?>) do not differ materially from 

 those of Cstellatus. 



Cirrus i has rami of 7 segments, the anterior ramus longer by two. 

 The posterior edge of the lower segment of the anterior ramus 



-^:^:^^:^^ 



Fig. 00. — Chthamalus cikratus, San Louuenzo Island, a, basal segments of the rami 



OF CIURUS II, THE ANTERIOR MARGIN TOWARD THE LEFT. h, EDGE OF THE MAXILLA. 

 C, ELEVENTH SEGMENT OF CIRRUS VI ; ONLY THE OUTER SPINE OF EACH PAIR IS DRAWN. 



bears a scries of about six obliquely conic teeth, reminding one of 

 those of x\ cast a. 



Cirrus ii has rami of 8 and G segments. The anterior ramus is 

 longer by about two segments, and on its lower segment bears a 

 series of conic teeth directed toward the posterior ramus (fig. OGa). 

 Several succeeding segments have one or two similar teeth. 



Cirrus iii has very unequal rarrvl of IG and 30 segments. Those of 

 the distal third of the longer ramus are very slender and bear only 

 a few slender spines near their distal ends. The other segments are 

 anned wdth six pairs of spines. Darwin states that he found the 

 rami equal in one specimen. The later cirri have subequal rami, the 

 segments bearing six pairs of spines (fig. IHx). 



There is not much variation in the opercular valves, but much 

 more in the wall. In one specimen from San Lorenzo Island the 

 wall is rather thin, not rlhhcd, and covered with a dark oJlve-hrown 

 cuticle in the lower part. The upper part is corroded. The interior 

 is smooth, and the sutures are distinct. The long slope of the articu- 



