230 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



a 2 . Much larger, rostrum about 18 mm. long; radii extremely narrow or want- 

 ing; tergum much wider than scutum, the spur occupying two-thirds of the 

 basal margin ; scutum with a well-developed adductor ridge ; sheath long, 

 two-thirds the length of the lateral compartments. West America. 



B. orcutti Pilsbry 

 BALANUS DECLIVIS Darwin. 



Plate 55, figs. 1-lfZ. 



1854. Balanus declivis DAKWIN, Monograph, p. 275, pi. 7, figs. 4o-4(Z. 

 1901. Balanus declivis Darwin var. cuspitlatius YEKKILL, Trans. Connecticut 

 Academy, vol. 11, p. 22. 



Type. British Museum. 



Distribution. Antillean faunal province, known from the follow- 

 ing localties: Fish Hawk Station 7300, oil Cape Sable, Florida, 11 J 

 feet, in a sponge. Bermuda, Louis Mowbray. It has also been re- 

 ported by Darwin from the West Indies (British Museum) and 

 Jamaica, in a sponge (Cuming collection, now in British Museum). 



The barnacle is fragile, the compartments being very weakly 

 cemented together; walls thin, not porose, basis membranous; ros- 

 trum boat-shaped, about twice as long as the other compartments. 

 Aperture toothed. Parietes smooth except for faint growth-lines 

 and in places some fine, oblique wrinkles or scalelike tuberculation ; 



gray or white under a very thin cartridge-bull' epidermis, which also 

 covers the opercular valves. Greatest diameter 6 mm., length of 



rostrum 9 mm. in the largest specimens.. 



The scutum is somewhat convex externally, but with a slight lon- 

 gitudinal depression in some examples, with sculpture of close, fine 

 growth-ridges, which are all continued on the occludent edge. The 

 ridges are very finely crenulated by longitudinal striae, sometimes 

 very faint, and in the best-preserved specimens are minutely bristly. 

 There is a narrowty triangular area or radius built out on the apical 

 half of the occludent edge. The articular ridge is rather strong, 

 two-thirds as long as the tergal edge or less, its lower end oblique. 

 There is the mere trace of an adductor ridge, or none, and a small, 

 lather deep depression for the lateral depressor muscle at the lower 

 margin. 



The tergum is about as wide as the scutum, somewhat beaked, 

 ciliated along the carinal border, which is well arched. Articular 

 ridge moderate, articular furrow wide. The spur is very short, 

 truncate, half as wide as the basal margin or slightly more. It 

 stands very close to the basiscutal angle. 



Compartments. The paries of the lateral compartment is wider, 

 sometimes three times as wide, as that of the carinolateral. The radii 

 are usually narrow but sometimes wide, not sunken or conspicuous, 

 but whiter than the parietes by lacking epidermis ; summits oblique. 

 The ala3 are rather wide with oblique summits and smooth edges. 



