70 BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



bb. Scutum entire basally . Atlantic S. dicheloplax. 



o.a. Carina with the roof flat or but shghtly concave; rostral latera narrow and 

 simple. 

 b. Umbo of the carina close to the apex; upper latus narrow, irregularly lunate; 

 scutum without a tergal calcified branch, the base bifurcate. Pacific coast. 



(S'. larvale. 

 bb. Umbo of the carina close to the apex; upper latus /\-shaped; lateral plates of 

 the lower whorl triangular, the inframedian latus very small. Japan. 



S. nipponense. 

 bbb. Umbo of the carina at the upper third or fourth of the plate; upper latus wide, 

 spatulate or subtriangular; scutum entire basally; inframedian latus very 

 narrow, 

 c. Umbones of carina and carinal latera prominently projecting. Atlantic. 



*S'. imperfectuin. 



cc. Umbones of carina and carinal latera hardly modifying the dorsal contour. 



Pacific coast .V. sanctsebarbarce. 



GROUP OF SCALPELLUM DICHELOPLAX. 

 SCALPELLUM DICHELOPLAX, new species. 



Ttjpe.~-C?it. No. 11951, U.S.N.M. 



Type-locality. — Albatross Station 2711, north latitude 38"^ 59', west 

 longitude 70° 07', in 1,541: fathoms. 



Other localities.— ^o. 32862, Station 2222, north latitude 39° 03' 15", 

 west longitude 70° 50' 15", in 1,537 fathoms, bottom temperature 

 36.9-. Nos. 8030, 8631, Albatross Station 2221, north latitude 39° 05' 

 30", west longitude 70° 44' 30", 1,525 fathoms, bottom temperature 

 36.9°. 



The capitulum is irregularly ovate and strongl}'^ compressed, com- 

 posed of 13 very imperfectly calcified plates. The occludent and 

 carinal margins are strongly and about equally convex. The plates 

 are all biramose or V-shaped, with the exception of the carina. The 

 cuticle is smooth, without pubescence or hairs. 



The scutum has a wide convex occludent and a ver}' narrow, curved 

 tergal calcified segment. The former is widest at the base, tapering 

 to about one-third that width in the upper portion. The surface is 

 sculptured with low, narrow, widely spaced riblets parallel to the basal 

 margin. The occludent margin is strongly convex; the umbo is ter- 

 minal at the apex, which is recurved within the ventral outline and 

 overlies the base of the tergum. 



The tergum is V-shaped, having a curved occludent branch about 

 twice as wide as the long, slender, and curved carinal branch. This 

 is nearly twice the length of the occludent branch. The apex is acute 

 and somewhat recurved. 



The carina is strongly arched, more so above. The umbo turns 

 inward, but is not quite terminal, a flattened continuation of the sides 

 extending beyond it. The roof is very deeply channeled, with high, 



