THE BARNACLES IN THE U. S. NATIONAL MUSEUM. 



49 



carinal margin is veiy weakly sij^inoid, being- coiicaNc in its upper 

 portion, convex in the lower. 



The carina is long", more arcuate near the terminal mucro. The roof 

 is fiat, with bordering ribs. The fine growth-striae across the roof are 

 com-ex upwardly. The sides are rather wide, regularl}" tapering 

 toward the base. The basal margin is slightl}^ concave. 



The upper lateral plate is hexagonal-pi riform. The scutal and 

 tergal margins are long and a little concave. The carinal margin and 

 that against the carinal latus are short and equal. The basal mar- 

 gin, against the summit of the inframedian latus, and the apical 

 border, against the latero-tergal lobe of the scutum, are ver}^ short. 

 The apex is subterrainal. 



There is no rostrum. 



The rostral latus is scjuare, a])out as high as wide. The margins are 

 straight. The lower lateral corner is rounded. The ventral margins 

 of the rostral latera are 

 in contact. 



The inframedian lat- 

 eral plate is wineglass 

 shaped, composed of a 

 ver}^ small basal and 

 large upper segment, 

 very narrow at their 

 j unction , \v here the 

 uml)0 is situated. The 

 upper margin has a 

 longer scutal margin 

 and a shorter margin in 

 contact with the upper 

 lateral plate. 



The carinal latus is twice as high as wide, of very irregular shape. 

 The um])o projec;ts slightly Ijeyond the carina, near the base of the 

 plate. The carinal latera meet below the keel. 



The peduncle is very short, with 10 rows of transversely lengthened 

 s<'ales, about 8 scales in a row. 



Length of the capitulum 18, ))readth 1) nun. Length of the peduncle 

 4.3 nuu. Length of the carina IT), diameter at base 3 mm. 



This species is well characterized by the wineglass-shaped infra- 

 median lateral plate and the peculiar contour of the inner margin of the 

 scutum. 



It is closely ndated to S. dlstinctuin Hoek, a Pacific species; but 



that has the scuta, upper latera, and rostral latera different in shape. 



S. car Inaf Hill Ho(»k, from off Tristan da Cunha, resembles S. idloplax 



in the shape of the scutum, upper latus, and inframedian latus, but it 



4715— Bull. 60—07 4 



l> 



Fk;. 15. — Scalpellum idioplax. ", lateral view X 2; b, rostral 

 view; f, dorsal view. 



