REPORT ON THE HEXACTINELLIDA. 255 



spicules from the delicate quadrate mcshwork, and are distinctly marked off from one 

 another by a somewhat sharp-edged, spicule-bearing border, extending down to the bushy 

 basal portion. Towards the external margin, the flat body which measures 3 to 5 cm. in 

 thickness, becomes gradually sharper ; the maximum height is 40 cm., and the breadth 

 about as much. The somewhat irregular knobbed base is continued into a bushy beard- 

 like basal tuft of spicules 10 to 12 cm. in length. By this the sponge is fixed among 

 the coral and other detritus (PI. XLIX.). 



The parenchymal skeleton consists of large or medium-sized smooth oxjr|[Dentacts, 

 which probably had their four tangential rays originally inserted in some bounding 

 surface, while the fifth stood radially. Afterwards, however, they came to be 

 embedded in the parenchyma. The angles of the five rays are generally, though by no 

 means always, right angles, and one or other of the rays not unfrequently exhibits a 

 simple curvature near its origin. The individual rays usually have a length of 10 to 20 

 mm. Throughout the whole parenchyma irregularly scattered, small, lank oxyhexacts 

 also occur, with rays of about equal length, straight or slightly curved, and usually some- 

 what roughened, i.e., beset with small pointed tubercles, which are occasionally longer, and 

 project obliquely outwards, as represented in PI. L. fig. 6. Less frequently uncinate 

 forms occur, but only near the two limiting surfaces, and usually in radial disposition. 

 Some uncinates only attain a length of 2 to 4 mm. (PI. L. fig. 3), but most are much 

 longer. The short, smooth, spindle-shaped oxydiacts, which occur so abundantly in the 

 parenchyma of Poliopogon gigas, to be described below (PI. XL VIII. figs. 3, 7), are here 

 wholly absent. 



The supporting spicules of the gastral skeleton are, as in all Hyalonematids, strongly de- 

 veloped, smooth oxypentacts of varied dimensions. Their radially directed ray may attain 

 a length of 1 to 2 cm., while the four tangentials, crossed approximately or exactly at right 

 angles, and but rarely bent, may be as long or longer, and are apposed to one another in 

 twos or threes to form the familiar quadratic lattice-work. The autodermal pinuli are 

 somewhat small pentacts about 0"4 mm. in length, with straight spines directed obliquely 

 upwards and outwards. The outer end of the distal ray passes into a long thin point ; 

 the basal portion is smooth. The four moderately long (O'l mm.) basal rays, are internally 

 smooth, but are on their outer halves beset with short, distant, outward directed teeth, 

 and end in slightly conical points. While disposed at right angles to the distal ray, they 

 do not form right angles with one another, but two opposite obtuse and acute angles, 

 with a slight curvature in the two acute angles so that the form of the central 

 portion of a 8 results (PI. L. fig. 5). Numerous eight-rayed amphidiscs of various size, 

 but of similar form occur in the dermal membrane, and appear to penetrate thence into 

 the parenchyma. The larger have the middle portion of their axis rod inserted in the 

 dermal membrane, while the one end projects freely to the exterior, and the other into a 

 subdermal space. Some of these have a length of 0"2 mm. and a moderate thickness, are 



