THE BARNACLES TN THE U. S. NATIONAL MUSEUM. 



41 



The capitulum is of the usual quadrate form, the plates separated 

 by narrow but distinct chitinous sutures, covered with a very thin, 

 smooth cuticle. The occludent border is straigfht, except near the 

 apex. 



The scutum is quadrangular, with straight occludent margin. The 

 length is about twice the width. Umbo at the acute apex. The sur- 

 face is divided into an anterior radially costate and a tergo-lateral 

 smooth area. 



The tergum is a little longer than the scutum. The occhident mar- 

 gin is convex above, the 

 apex being recurved. 

 The scuto-lateral margin 

 is slightly convex, the 

 carinal margin nearly 

 straight. 



The carina is regularly 

 and rather strongly 

 curved, with the umbo 

 terminal. The roof is 

 deeply groved ])etween 

 strong sulcate ])ordering 

 ribs. The sides are rather 

 narrow and of nearly 

 equal width throughout. 



The upper lateral plate 

 is quadrangular, the scu- 

 tal margi n longest, 

 slightly concave, paral- 

 lel to the carinal mar- 

 gin. Tergal margin 

 straight. Basal mai'gin 

 oblique. The scutal half 

 of the plate is sculptured 

 with a few radiating 

 ri})lets. Umbo at the 

 apex. 



The rostrum is triangular, very small and short, somewhat wider 

 than high. 



The rostral latus is low, the length of the plate being more than 

 four times its width. The upper and lower margins are parallel. 

 An angle runs obliquely from the beak toward the baso-lateral angle. 



The inframedian latus is quadrangular, with one of the upper 

 angles produced toward the carina. The umbo is subcentral, a little 

 nearer the rostral margin; from it a rib runs to each of the angles of 

 the plate. 



Fig. U.— Scalpellitm rathbun.k. n, rostral, h, carinal, and 



C, lateral views of type X 2; (1. INFRAMEDIAN LATUS OF 

 ANOTHER INDIVIDUAL X 4. 



