330 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The absence of terminal appendages is perhaps a more important 

 character, differentiating Hexelasma from Pachylasma; yet these 

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

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

 minute joint, with minute terminal bristles. 



Since the rostrum of Hexelasma overlaps the adjacent latera, 

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

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

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

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

 lasma slightly over 1 mm. in diameter. 



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

 Hexelasma, belongs to the Chthamalid(L', 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. 



Ilexelasma now contains seven species, as follows : 



H. velutinum Hoek. Malay Archipelago, 204 to 390 meters. 



II. arafurcc Hoek. Malay Archipelago, 560 meters. 



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



H. hirsutum Hoek. Faroe Channel, 930 meters. 



H. aucklandicum Hector. 1 New Zealand, Miocene. 



And the folloAving collected by the Albatross: 



HEXELASMA AMERICANUM, new species. 



Plate 69. 



Type. Cut. No. 14559, U.S.N.M. 



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

 tude 29 39' north ; longitude 79 49' 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 ala?. 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 growth-marks being minutely 

 rippled and longitudinally a little roughened. The sheath is salmon 

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



ir T. II. Withers, Proc. Zool. Soc. London, 1913, p. 841, pi. 85. The detached compart- 

 ments of this gigantic species were originally referred to ScalpcUum. Its proper generic 

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



