88 BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



MEGALASMA GRACILE GRACILIUS, new subspecies. 

 Plate V, fig. 16. Plate VII, figs. 6, 7, 8, 9. 



Type.— Cdit. No. 11346, U.S.N.M. 



Type-locality. — From AUxitross Station 2625, between Cape Hatteras 

 and Charleston, South Carolina, on spines of Dorocidarh j)ttpmit(i., 

 No. 12938, 247 fathoms. 



Other localities.— Cat No. 32900, U.S.N.M., Alhatross Station 2658, 

 between the Bahamas and Cape Fear, North Carolina, on ScaljjeUuat 

 giganteuin Gruvel, in 514 fathoms. 



The capitulum is twice as long as wide, widest in the middle, 

 stronoiy inflated just below the middle, compressed above the infla- 

 tion. The carinal border is much more convex than the occludent. 

 The plates are sculptured with fine and very inconspicuous radial stride 

 and rather coarse wrinkles and occasional grooves along the lines of 

 growth. The basal foramen is subcircular and small. 



The scutum has a moderately curved occludent margin and very 

 short basal margin. The straight tergal margin is slighth' shorter 

 than the carinal, which is convex, except near the base, where it is 

 somewhat concave. A sharp keel runs from the umbo to the apical 

 angle, and a strong angle to the tergo-carinal angle. The area in 

 front of the keel is very narrow, with its fellow forming a narrowly 

 lanceolate figure in ventral view. Internally there is a very small 

 umbonal tooth in each valve and a small polished basal area of attach- 

 ment of the peduncle, but no basal callus. (Fig. 7.) 



The tergum is rhombic, its carinal margin about one-third as long 

 as the occludent. Its surface is divided into two unequal areas by a 

 diagonal line from the apex to the baso-carinal angle, the larger area 

 being grooved lengthwise of the plate, the narrow upper area marked 

 with lines at right angles to the other. 



The carina (figs. S, 9) is moderately and evenly curved, with a flat 

 roof. The umbo projects beak-like far beyond the base of the 

 scutum. The basal margin of the carina is fully as long as thafof 

 the scutum and forms a right angle with it. The sides of the carina 

 are very wide in the basal third and are obliquely grooved. Inside 

 the carina is slightly concave throughout, and a narrow cavity pene- 

 trates downward to the apex, behind a concave plate which extends 

 over the basal region of the cavity. This plate becomes narrower 

 above, is truncated, and its sides project to form two blunt teeth. 



The peduncle is extremely short, about one-tenth the length of the 

 capitulum, and scarcely extending beyond the umbo of the carina. It 

 is transversely wrinkled and blackish. 



Length of the capitulum (measured to the umbo of the carina) 

 11.8 mm., width 5 mm., diameter 3 mm. Length of the carina 

 7.75 mm. 



