THE SESSILE BARNACLES. 



305 



This subspecies is described by Darwin as follows: 



Shell much depressed, surface much corroded, smooth; ;il;c largely exposed, 

 marked by lines of growth ; radii not present ; parietes on the under side often 

 supported by pillars; orifice subhexagonal. Diameter up to three-quarters of 

 an inch. Tergum very narrow. 



This variety or subspecies is known from the Bay of Naples (type- 

 locality), Straits of Gibraltar, and St. lago, Cape Verde Islands, 

 where it occurs associated with stellatus. It is not present in the 

 museum, and is included here for comparison with the following 

 form, which is rather similar in the shape of the opercular valves. 



CHTHAMALUS STELLATUS ANGUSTITERGUM, new subspecies. 



Plate 71, figs. 5-5 &. 



Type. Cat. No. 48199, U.S.N.M., from the Bahamas. 



The walls are deeply corroded above, irregularly ribbed near the 

 base, as in stellottts; interior roughened, more or less purple-tinted. 



The scutum has 

 a straight articular 

 rib, truncate at the 

 lower end. The 

 adductor muscle pit 

 is very shallow; no 

 adductor ridge. 

 Pit for the lateral 

 depressor deep. 



The tergum is 

 very narrow and 

 thick. There is a 

 small but distinctly developed spur, much narrower than in fragilis; 

 basal margin concave; crests very strong. From its thickness the 

 tergum is triangular in transverse section. It is seen rolled toward 

 the right in plate 71, figure 55, showing the broad scutal articulating 

 face. In figure 85 a direct view of the inner face is given. 



The opercular valves are white or pink inside. 



The labrum has a concave edge with teeth along the median por- 

 tion (fig. 865). 



The mandible and maxilla are very similar to those of C. stellatus, 

 shown in figures 84c, d. 



Cirrus i has rami of 7 and 5 segments, the anterior longer by two 

 segments. 



Cirrus ii has 6 and 5 segments, the anterior ramus longer by two. 

 There are no large pectinated spines. 



Cirrus iii has rami of 12 and 14 segments, the lower ones having 

 six pairs of spines, the rest five pairs. 



FIG. 85. CHTHAMALUS STELLATUS ANGUSTITEKGUM. SCUTUM 

 AXD TERGUM OF THE TYPE. 



