398 Mr. II. J. Carter oti Deep-sea 



into the lobes respectively of the petrous crust. Vents in the 

 cribritbrm structure at tlie bottom of tlie deep depressions 

 of the surface. Internal structure consisting of a circum- 

 ferential zone of spicules arranged parallel to each other 

 and ])erpendicular to the body-substance on winch their 

 pointed ends rest, Avhile their heads support the petrous 

 crust of siliceous balls ; composed of the " zone-spicule " par 

 excellence (fig. 45, a), tlie " body-spiculc " (fig. 45, c), and 

 the two forms of " anchoring-spicule " (fig. 45, d). Body- 

 substance composed of the " body-spicules " alone, held toge- 

 ther by areolar sarcode charged more or less with flesh- spicules, 

 and traversed by the branches of the excretory canal-system. 

 Excretory canal-system most developed towards the circum- 

 ference, least towards the centre of the body-substance, where 

 the spicules are most densely aggregated and the structure 

 most compact, whence the subnucleated appearance. Skele- 

 ton-spicules of three forms, viz. :— 1, the zone-spicule, com- 

 posed of a long, stout, straight shaft, smooth, round, sharp- 

 pointed, and directed internally, supporting a head consisting 

 of three arms, furcated, expanded horizontally, and a little 

 recurved, su})porting the petrous crust externally, shaft 170- by 

 8-1800ths incli, total expansion of the arms 54-1800ths inch in 

 diameter (tig. 45, a) ; 2, body- or staple spicule, acerate, stout, 

 more or less curved, smooth, round, attenuatingly pointed, 

 mixed with the zone-spicules, where it often pierces the 

 crust, and forming, with the exception of the siliceous balls in 

 all stages of development and the body-stellates exclusively, 

 the skeleton-spicule of the body-substance, 190- by 5-1800ths 

 inch (fig. 45, c) ; 3, anchoring-spicule, composed of a long, 

 delicate, straight shaft, smooth, round, sharp-pointed, and 

 directed internally, supporting a small head with usually three 

 delicate arms recurved like the flukes of an anchor, or extended 

 like the prong of a fork (fig. 45, d), associated with the zone- 

 spicules, but often piercing the petrous crust so as to form 

 anchoring-spicules externally, w^hich are for the most part 

 broken off, shaft very long and thin, variable in length, arms 

 about 9-1800ths inch long. Flesh-spicules of four forms, 

 viz.: — 1, the nodastrellum, globular, the rays being repre- 

 sented by minute round tubercles about 2-6000ths inch in 

 diameter, hence its name, most abundant in the dermal reticu- 

 lation (fig. 45, (J, k) : 2, dermal, acerate, slightly curved, 

 smooth, round, attenuatingly pointed, supporting the dermal 

 reticulation over the petrous crust, about 22- by ^- 1800th inch 

 (fig. 45, ?i) : 3, siliceous ball, spheroidal or elliptical (fig. 45,/), 

 slightly compressed, presenting, when fully developed, a tessel- 

 lated stelliferous surface, and a hiluin-like depression on the 



