THE SESSILE BARNACLES. 



305 



This subspecies is described by Darwin as follows : 



Shell much depressed, surface much corroded, smooth ; al;e largely exposed, 

 marked by lines of gi-owth ; radii not present ; parietes on the under side often 

 supported by pillars ; orifice subhesagonal. Diameter up to tlu-ee-quarters of 

 an inch. Tcrgum very narrow. 



This variety or subspecies is known from the Bay of Naples (tyj^e- 

 locality), Straits of (libraltar, and St. lago, Capo A^erde Islands, 

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

 museum, and is included here for comparison Avith the following 

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



CHTHAMALUS STELLATUS ANGUSTITERGUM, new subspecies. 



Plate 71, figs. 5-5&. 



Type.— Cat. No. 48109, U.S.N.M., from the Bahamas. 



The walls are deeply corroded above, irregularly ribbed near the 

 base, as in steJIatus/ 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 mid ^'''^'- ^^• 

 thiclv. There is a 

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

 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, shoAving 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 Avith teeth along the median por- 

 tion (fig. 8G&). 



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

 showm in figures 84(?, d. 



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

 segments. 



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

 There are no large pectinated spines. 



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

 six pairs of spines, the rest five pairs. 



-ChTHAMALUS STELLATUS ANGUSTITERGUM. 

 AND TERGUM OF THE TYPE. 



