3S0 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The absence of terminal appendages is perhaps a more important 

 character, differentiating Hexelasma from P actiylasina ; yet these 

 vary a good deal in Pachylasma. In P. crinoidophilum the appen- 

 dages have eight joints; in P. darwinianum only one extremely 

 minnte joint, with minute terminal bristles. 



Since the rostrum of Uexelasma overlaps the adjacent latera, 

 which have ala?, it is certainly a composite plate formed of the con- 

 crescent rostrum and rostral latera, exactly as in Pachylasma gUjan- 

 teum. Young specimens, when found, should be examined for 

 traces of the sutures. Darwin found them at the apex in a Pachy- 

 las7na slightly over 1 mm. in diameter. 



The form of the labrum and of the third cirri show at once that 

 Hexelasma belongs to the ClithanrialkUv^ and not to the Ba- 

 lanidw. The armature of mandible and maxilla, the form of the 

 lower edge of the sheath, and the texture are also characters pointing 

 in the same direction. 



Hexelasma now contains seven species, as follows : 



H. velutinwin Hoek. Malay Archipehago, 201 to 390 meters. 



H. arafurm Hoek. Malay Archipelago, 5C0 meters. 



H. corolliforme Hoek. Near Kerguelen Island. 270 meters. 



H. hirsutum Hoek. Faroe Channel, 930 meters. 



H. auchlandiemn Hector.^ New Zealand, Miocene. 



And the following collected by the Albatross: 



HEXELASMA AMERICANUM, new species. 

 Plate G9. 



Type.— Q?it. No. 14559, U.S.N.M. 



Type-locality. — Alhatross station 2G63, off South Carolina, lati- 

 tude 29° 39' north; longitude 79° -19' west; 421 fathoms, bottom tem- 

 perature 42°.7 F., seated on a branch of coral. 



The barnacle has a membranous basis with narrowly inflected cal- 

 careous borders; strong, solid compartments which are only weakly 

 cemented together, are without pores, and have no radii. Light buff 

 or delicately salmon tinted under a very thin pale corneous cuticle, 

 which extends over the parietes and part of the alae. The orifice is 

 rather small and deeply notched. The alae are broad, regularly ob- 

 liquely striated, and have very oblique, smooth summits. The parietes 

 have distinct, spaced linear growth-marks, which on some of the 

 plates show an indistinct and minute puckering (possibly indicative 

 of deciduous hairs) ; the surface between growtli-marks being minutely 

 rippled and longitudinally a little roughened. The sheath is salmon 

 buff, smoothly grooved transversely, less than half as long as the 



IT. II. Withers, I'roc. Zool. Soc. London, 1913, p. 841, pi. 85. The detached compart- 

 ments of this Kii^antic species were originally referred to ScalpeUum. Its proper generic 

 reference is due to Mr. Withers. It attained a length of 19 cm. 



