THE SESSILE BARNACLES. 329 



PACHYLASMA GIGANTEUM (Phllippi). 



1854. Pachylasma (jUjantciiin I'liilippi, Darwin, Monograph, p. 477, pi. 19, 

 figs. 5a-5d. 



Cat. No. 120G0. Strait of Messina. Seguenza, in Jeffreys collection. 



PACHYLASMA DARWINIANUM Pilsbry. 



1912. Pachylasma darwinianum Pilsbry, Proc. U. S. Nat. Mus., vol. 42, p. 

 293. 



Type.— Cut No. 434G5, U.S.N.M., from Alhafross Station 5108, 

 Tawi Tawi gronp of the Suln Archipelago, 80 fathoms. 



PACHYLASMA CHINENSE Pilsbry. 



1912. Pachylasma chinense Pilsbry, Proc. U. S. Nat. I\Ius., vol. 42, p. 293. 



Type.— Cat No. 43471, U.S.N.M., from Albatross Station 5301, 

 China Sea, near Hongkong, 208 fathoms. 



PACHYLASMA CRINOIDOPHILUM Pilsbry. 



1911. Pachylasma crinoidophilum Pilsbry, Bull. Bui-oau of Fisliorit^s, vol. 

 29, p. 81, fig. 11 ; pi. 17, figs. 1-11. 



Type.— Cat No. 38675, U.S.N.M., from Albatross Station 4934, 

 off Kagoshima Gulf, in 152 fathoms. 



Genus HEXELASMA Hoek. 

 1913. Hcxclasma Hoek, <Si?>Oi/r/-Expeditie, JMonographie 31ft, pp. 157, 244. 



Hoek described this genus as follows : 



Compartments six ; carina, carinolateral an<l lateral oompartmonts with 

 alae, but without radii, the rostrum having neither radii nor al*. Parietes not 

 porous and without longitudinal rihs on their inner surfaces. Basis mem- 

 branous. Opercular valves subtriangular. Mouth with the labrum not notched 

 in the middle; mandibles with 4 to 5 sharply pointed teeth; maxilhe with 

 numerous spines beneath the notch. Third pair of cirri resembling more 

 those of the fourth than of the second pair. No caudal appendages. Species 

 living in deep water. 



By the texture of the compartments and valves, the absence of 

 radii and the absence of an adductor ridge in the scutum, Ilexelasma 

 resembles Pachylasma; but it differs by having no trace wliatever of 

 caudal appendages, and in the typical species by having a mem- 

 branous basis. In H. aTne/icanum and 11. eallhtodermii the Ijasis is 

 calcareous, but very thin in the center, so that in specimens removed 

 from the support the very thin, filmlike central region adheres 

 partly to the support, so tliat I formerly desci-ibed caHhtoderma as 

 having the central part ol' the basis membranous. There is an in- 

 flected rim at the bases of the compartments very much thicker than 

 the true basis. 



