Synojisi'^ of the Australian Galcarea Heterocoela. 91 



about half the thickness of the chamber layer ; the apical ra\' 

 projecting into the gastral cavity, almost in a line with the 

 basal ray. The basal ray is long, straight, and gradually 

 sharp-pointed, about ()"28 by O'Ol mm. ; the oral rays are 

 short, straight, conical and gradually sharp-pointed, about 

 0*056 by 0008 mm. ; the apical ray is slender, conical, 

 elongated, slightly curved and finely pointed, about 0O9 by 

 0-007 mm. (3) Tubar triradiates ; consisting almost entirely 

 of the strongly developed, centrifugaliy directed basal ray^ 

 which is straight, fusiform, gradually sharp-pointed at the 

 distal end, and at the proximal end provided with a pair of 

 minute, widely divergent, conical teeth, which represent the 

 extremely reduced oral rays. The basal ray measures about 

 0-3 by O'OOS mm., while the teeth representing the oral rays 

 are only about 003 mm. in length. The entire tubar 

 skeleton is made up of these spicules and the basal rays of 

 the subgastral quadriradiates, arranged usually in single 

 series but with overlapping ends, each series comprising only 

 about three spicules. (4) Triradiates of the dermal cortex ; 

 very lai'ge and stout and regularly sagittal, the oral angle 

 being very considei-ably wider than the paired angles ; all 

 the rays are straight, conical and gradually sharp-pointed, 

 the oral rays measuring about O'o-t by 0-07 mm., and the 

 basal ray somewhat shorter and slenderer. These spicules 

 are arranged in many layers, parallel to the dermal, surface 

 and extending through the entire thickness of the cortex. 



(5) Dermal oxea ; short, slender, slightly crooked, sharply 

 pointed at each end, about 01 by O'OOO mm. These spicules 

 occur in large numbers on the dermal surface, projecting at 

 right angles from the outermost portion of the cortex. 



(6) Oxea of the oscular fringe ; long, straight and slender, 

 gradually sharp-pointed at each end though hastate at the 

 outer end. These spicules form a kind of vertical palisade 

 inside the margin of the osculuin, their outer ends project- 

 ing to form a feebly developed oscular fringe. (7) Oscular 

 triradiates : closely resembling the remarkable tubar tri- 

 radiates, but A\-ith the oral rays not quite so much reduced. 

 These spicules occur mixed with the inserted portions of the 

 oscular oxea, and assist the latter in forming a dense 

 ]:»alisade ; the paired raj'S are directed towards the osculum, 

 and no part of the spicule projects freely like the oxea do. 



This sponge is decidedl}^ the gem of Mr. Wilson's collection. 

 The exquisite symmetry of the skeleton and canal-system, 

 combined with the remai-kable spiculation, render it one of 



