332 BULLETIN 03, UNITED STATES NATIONAL MUSEUM. 



The tergum is nearly flat, weakly striate transversely, the carinal 

 half slightly convex and scored with a few longitudinal lines. A 

 weakly impressed line runs to the carinal base of the spur, which 

 has no furrow. The spur is very short, occupying about one-third of 

 the basal margin. It is close to the basiscutal angle, and its end 

 is obliquely truncate. Inside there is a rather low but long articular 

 ridge, and numerous sharp but short crests for the depressor muscle. 



The mandible has four rather acute teeth and a spinose lower point. 



The maxilla has two large spines followed by a notch in which 

 there are several small ones. Median third is armed with long but 

 unequal spines and the lower fourth with shorter spines (fig. 986?) . 



This peculiar barnacle is obviously related to Ilexelasma callisto- 

 derma (Pilsbry) of the western Pacific, agreeing with that in the 

 structure of the walls and opercular plates, the slender teeth of the 

 mandible, the strongly annulate, rather short and hairless penis, and 

 the structure and spines of the cirri. It differs from the Pacific 

 species by having a narrower scutum, while the tergum is somewhat 

 wider, Avith longer basal and shorter carinal margins; the spur is 

 shorter and scarcely separated from the basiscutal angle of the 

 valve. The external sculpture of the compartments is also less 

 developed in the Atlantic species, which moreover differs by the 

 flattened side walls and various other peculiarities of the wall plates, 

 such as their minute sculpture. 



The material examined consists of one perfect individual (Cat. No. 

 14559) from the type-locality, and parts of at least three incomplete 

 ones (detached plates of the wall) from a lot labeled as from Alba- 

 tross stations 2662-3-9, 2671-2 and registered as Cat. No. 48093, 

 U.S.N.M. 



The remains of two individuals in No. 48093 show carince similar 

 to that of the type, except that they are a little less bowed, the roof 

 being flattened (pi. 69, fig. 3). 



In the third individual (pi. 69, fig. 2) the carina is almost straight, 

 narrow, and nearly parallel-sided, w^ith the roof very convex. From 

 the shape of the basal margin it is clear that this one grew upon a 

 narrow branch of the coral, with its carinorostral axis parallel to 

 that of the branch. The whole contour of the barnacle was doubtless 

 modified b}^ the narrow support. 



HEXELASMA CALLISTODERMA (Pilsbry). 



1911. Balanus caUlstoilcrma Pilsbry, Bull. Bureau of Fisheries, vol. 29, 

 p. 78, fig. 10, pi. 12, fig. 5 ; pi. 15, figs. 3-7. 



Type.— Cat No. 38690, U.S.N.M., from Albatross station 5068, 

 Suruga Gulf, Japan, in 77 fathoms. 



