REPORT ON THE HEXACTINELLIDA. 167 



distinction from Aulochone, that from the lower portion of the gastral cavity no canal 

 leads downwards into the stalk, but that the floor of the gastral cavity has the same 

 parenchymatous structure as the lateral wall, and exhibits the same round canalicular 

 apertures as in the latter. The stalk is not a tube with a simple canalicular lumen as in 

 Aulochone, but is penetrated by an irregular lacunar and canalicular system, which opens 

 superiorly into the efferent canal system of the lower portion of the body. 



The greater part of the parenchymal skeleton consists of long, straight or slightly 

 curved, smooth diacts, with or without central nodes, and with rough club-shaped ends 

 (PI. LXVII. figs. 2, 3). They occur either in isolated distribution or in strands. Between 

 these a large number of oxyhexasters occur, in which the comparatively short and strong 

 principal rays bear from two to four diverging, long, strongly developed terminals. The 

 extremities of these terminal rays are never bent in hook-like fashion as in Crateromorpha 

 ■murrayi and Crateromorpha thierfelderi. Sometimes one or other of the principal rays 

 remains undivided, and not unfrequently both the rays on one axis, so that the latter 

 extends in a simple straight course to a pointed extremity (PI. LXVII. fig. 5). Between 

 these very numerous oxyhexasters, many-rayed discohexasters occur in very much less 

 abundance, but of about the same size as the former. Each of the short principal 

 rays bears about eight straight, substantial, cylindrical terminals, which are of equal 

 length, and extend, with uniform divergence, radially outwards. On their extremities 

 they bear convex, marginally toothed, transverse discs (PI. LXVII. fig. 6 ; Pl. LXVIII. 

 fig. 2). 



The hypodermalia of the dermal skeleton are moderately large pentacts, with straight, 

 cylindrical, generally smooth, but terminally roughened and somewhat club-shaped rays. 

 The tangential rays are disposed at right angles to one another and to the proximal radial 

 ray. 



The dermal membrane itself contains autodermalia in the form of cruciate tetracts, 

 with rough cylindrical rays, which are usually simply rounded off at their extremities, or 

 less frequently swollen in club-shaped fashion. Diacts also occur, with rays crossed 

 at right angles, and with or without four or two central protuberances. Sometimes, 

 through the abortion of one of the tetract rays, a triact form results (PI. LXVII. 

 fig. 4). 



The gastral and canalicular skeleton is destitute of hypogastralia and hy]3ocanalaria. 

 It consists of rough pentacts, with rays crossed at right angles, and rounded ofi' or some- 

 what swollen at their extremities. 



The spicules of the stalk do not difter from the corresponding forms in the body 

 proper (PI. LXVIII. fig. 2). In the lowermost portion of the stalk, however, there is, 

 by means of synapticula, a more or less extensive amalgamation and connection of 

 the long diacts, which are longitudinally disposed in approximately or perfectly parallel 

 courses (PI. LXVII. fig. 8). 



