THE BARNACLES IN THE U. S. NATIONAL MUSEUM. 69 



ing beyond the carina, the umbo being at the junction of the straight 

 and convex portions. The other three facets of the plate, resting re- 

 spectively against the peduncle, the inframedian latus and the upper 

 latus, are straight and about equal. Posteriorly the two carinal latera 

 are tricostate below the base of the carina, meeting there in a zigzag 

 suture. 



The peduncle is very short, conic, and covered with large imbricat- 

 ing scales, in eight rows of five or six scales each. 



Length of the capitulum 9, breadth 3,5 mm. Length of the 

 peduncle 1.5 mm. Length of the carina 7.2, diameter at base 1.4 mm. 



This little species is narrow^er than any closely related forms. S. 

 gracile has a much better developed rostrum, the occludent border is 

 convex, and the carina differs. The very narrow inframedian lateral 

 plate and the peculiar shape of the carina are also characteristic. A 

 colony of eight individuals, three of them young, was grouped upon 

 a slender stem, perhaps of a gorgonian. (Fig. 27.) 



VI. Section NEOSCALPELLUM. new section. 



Plates of the ca])ltulum, only yartlaUy calcified^ the calcareous 'por- 

 tion of the tergum V-shaped; inframedian latus narrow^ higher than 

 wide; scutum with apical umbo. Type, S. dlcheloplax. 



This section was established by Hoek in his memorable Challenger 

 Report, though it was not named at that time. 



The primary division in his key into species with the lower whorl of 

 plates perfectly, and those with them imperfectly calcified is faulty, 

 since it would separate immature from adult forms of the same species. 

 (See S. larvale on page 78.) It remains to be seen whether the group is 

 a natural one or whether it consists of species derived from several 

 phyla. A comparative stud}^ of series of young individuals may throw 

 light upon this inquiry, since these retain an earlier form of the plates. 

 Hoek found the complemental males of Scaljjelhan marginatum (a 

 species falling into the first division of my key) more degenerate than 

 those of S. intermedium, a species of my second division. 



S. Inerme Annandale is certainly not related to species of either 

 division of this section. It represents a parallel line of differentiation 

 from S. stearnsU Pilsbry, as Hoek has already recognized. Imper- 

 fectly calcified species occur in other phyla, such as S. patagonlcum^ 

 belonging to Scalpellum s. str., and S. giganteum, a species of 

 Holoscalpellum. 



KEY TO SPECIES. 



a. Carina with the narrow roof deeply guttered between high lateral ribs; the other 

 plates with the calcified portions biramose or triramose (group of S. dichelo- 

 plax. ) 

 b. Scutum bifurcate at the base. Pacific ....S. phantasma. 



