68 



BULLETIN GO, UNITED STATES NATIONAL MUSEUM. 



ing the excessively rudimentary rostrum) f ullv calcified plates, which 

 are smooth except for faint growth lines and very inconspicuous 

 radial striae. Cuticle hardly perceptible, smooth. Sutures linear. 



The scutum is more than twice as long as wide, with slightly convex 

 occludent and lateral margins. It is widest at the middle. The basal 

 margin is at right angles to the occludent. The tergal margin is very 

 oblique. 



The tergum is triangular, conspicuously longer than the scutum and 

 much greater in area. Its occludent and basal margins are subequal 

 and straight. The upper half of the carinal margin is straight, the 

 lower half convex. The apex is erect. 



The carina is long, rather strongly arched in its upper half, less so 

 in the lower half. 



The umbo is apical. The roof widens rapidly downwards; at first, 

 near the apex, it is convex, but it soon becomes flat, and even a trifle 



concave near the base, with 

 bluntly angular borders. The 

 sides are quite wide in the 

 apical third, but very narrow 

 and a little turned in in the 

 lower two-thirds. The basal 

 margin is convex. 



The upper lateral plate is 

 quadrangular, the scutal mar- 

 gin longest, concave, the beak 

 or umbo at its upper end en- 

 croaching a little upon the 

 scutum. The tergal margin 

 is a trifle convex, and slightly 

 longer than the carinal. The 

 basal angle of the upper lateral plate meets the baso-lateral angle of 

 the scutum, and the upper interior angles of the rostral, inframedian 

 and carinal latera; the sutures all radiating from a common center. 



The rostrum in most examples (as in the figured type) is a distinct 

 linear plate, clearly visible, though very narrow. In some examples 

 it is hardl}^ to be made out. The rostral latus is about as high as wide, 

 quadrangular, the ventral and lateral margins nearly equal and diverg- 

 ing upwards, the basal very short, about half the length of the others, 

 the scutal margin longest, slightly concave. The umbo has a tendency 

 to project slightly at the ventral l)Order. 



The inframedian latus is as long as the adjacent border of the rostral 

 latus, extremely narrow, wider at the base. Umbo at the apex. 



The carinal latus is long and narrow, its length fully twice the 

 width. The upper half of the carinal margin is straight, where in 

 contact with the sides of the cariha; the lower half is convex, project- 



FlG. 27.— SCALPELLUM GALAPAGANUM. a, LATERAL 

 VIEW, X 4, WITH 6, DETAILS OF ROSTRUM, AND C, 

 CARINA. 



