THE BAENACLES IN THE U. S. NATIONAL, MUSEUM. 



71 



narrow bordering ribs. The sides are rather narrow and of nearly 

 equal width throughout. 



The upper lateral plate is irregularly hexagonal, with the calcified 

 portion broadly V-shaped, the two branches nearly equal, somewhat 

 curved. A narrow appendage or third branch arises at the apex and 

 runs toward the tergum in a direction at a right angle to the tergal 

 branch. 



There is no rostrum. 



The rostral lateral plate is V-shaped, the basal branch of the V being 

 shorter and wider. 



Fig. 28.— Scalpellum dicheloplax. o, 6, Lateral and carinal views of the type, natural 

 size; c, young individual, natural size; d, S. dicheloplax BENTHOPHILA X 2. 



The inframedian latus is quadrangular. The rostral border is 

 longest, a little concave near the base, convex above. The upper 

 angle rests against the scutum. The oblique upper margin is a little 

 concave, larger than the basal margin, and about the same length as 

 the carinal. The straight basal margin is full}^ half as long as the 

 rostral. The carinal margin is a trifle concave. The calcified portion 

 is somewhat wineglass-shaped, being very narrow below the middle. 

 The base is a little expanded, and the upper part composed of two 

 diverging branches, that toward the scutum longer. The umbo is at 

 or below the lower fourth in the adult stage, but higher in the young. 



