150 THE VOYAGE OF H.M.S. CHALLENGER. 



an adjacent ray. We have, besides, to note the (sometimes very regular) occurrence of 

 a protuljerance between the bases of the rays, which is occasionally drawn out into a 

 long radially projecting spine. Or it may be that besides the six principals divided 

 into terminals other independent rays are present, running out into simple points 

 (PI. LVII. fig. 4). 



Finally, the parenchyTna includes a tolerable abundance of very minute disco- 

 hexasters, which are in some regions disposed with especial thickness below the external 

 and under the gastral skin. In these small discohexasters the short simple principals 

 bear broad, plano-convex, transverse terminal discs, from the convex external surface of 

 which numerous delicate divergent terminals arise, which are of equal length, and bear 

 minute transverse discs like those in the rosettes of other sponges as figured in PI. LVII. 

 fig. 11, PI. LXI. fig. 7, PI. LXV. fig. 4. 



The greater part of the dermal skeleton consists of autodermal tetracts, in which the 

 rays, intersecting at right angles, and inclined slightly inwards, are cylimlrically 

 thickened, or even somewhat club-shaped at their rounded extremities, and are beset 

 throughout their entire length with fine spines (PI. LVII. fig. 6). In many places, and 

 especially in the hillocky elevations, from which the radial spines project, besides these 

 autodermal tetracts, pentacts also occur in which the four tangential rays are altogether 

 similar to those of the tetracts, while a fifth proximal ray, springing from the node of 

 intersection, projects in a radial direction inwards (PI. LVII. fig. 7). Between these 

 tetracts and pentacts isolated smooth tetracts occur, double the size of the others, and 

 with their rays intersecting at right angles. 



The gastral skeleton consists of small gastral pentacts, which correspond exactly to 

 those of the dermal skeleton. Between these there is a sparse occurrence of tetracts also 

 like the dermal forms (PL LVII. fig. 2). 



Genus 5. Batlujdorus, n. gen. (Pis. LVIIL, LIX.). 



Saccular or bladder-shaped forms, with thin loose walls, smooth or spinous external 

 surface, and thin round oscular margin, which is (always Vj provided with a cufi-like 

 fringe of projecting spicules. The parenchyma contains, besides large diacts and hexacts 

 of various kinds, oxyhexasters and in some species discohexasters. The dermal skeleton 

 includes, besides the familiar smooth hypodermal oxypentacts, autodermal oxytetracts, 

 and in some species similar diacts or even monaets. In the gastral skeleton, on the other 

 hand, only roughened oxyhexacts occur. 



