1G2 THE VOYAGE OF H.M.S. CHALLENGER. 



exliibited by these forms of Crateromorpha, and by the great majority of the spirit-pre- 

 served Hexactinellida here described. It is noteworthy that the marginal fringe which 

 surrounds the superior circular opening (about 40 mm. in width) is not yellow, but 

 usually white. The stalk also appears somewhat lighter in colour than the dark grey- 

 yellow body-wall (PI. LXI. fig. 1). 



The main mass of spicules in the parenchyma of Crater omm'pha meyeri consists, 

 as in Batliydorus and Bhabdocalyptns, of long thin diacts, which are roughened termin- 

 ally, and exhibit either rounded off or bluntly pointed extremities. Some spicules bear 

 a distinct central thickening, or four cruciate, or less frequently two opposite hemispherical 

 tubercles, while the others exhibit no trace of such structures. The diacts vary greatly 

 in length and thickness, and are sometimes thickened terminally in a slightly club-shaped 

 fashion. Less frequently they are gradually narrowed and finally terminate in points, 

 while the middle portion is so thickened that the whole spicule acquires a spindle-shaped 

 form. Between these diacts of various length, medium- and small-sized oxyhexacts occur 

 in irregular distribution. In these the rays are frequently of considerable length, and 

 are uniformly narrowed towards the extremity, finally terminating in a point. 



There is an abundant occurrence of oxyhexasters with very short, sometimes 

 almost aborted, principal rays, and long slender terminals, which are usually bent 

 slightly outwards at the base, but are otherwise straight up to their pointed extremities. 

 Each short principal bears two to four of these terminals. Less frec[uently, and chiefly 

 on the subgastral trabecular s^^ace, small discohexasters occur, in which the moderately 

 short principal rays are terminally expanded into a transverse disc. The convex surface 

 of this disc bears a brush-like tuft of fine terminal rays, with toothed transverse discs on 

 their extremities (PL LXI. fig. 7). 



The dermal skeleton includes medium-sized hypodermal oxypentacts, with moderately 

 long and strongly developed straight rays, which are roughened near the extremity, but 

 are elsewhere smooth. The four tangential rays, which are cruciately disposed round 

 a central node, are at first slightly expanded and decrease gradually in thickness 

 towards the pointed ends. Besides these hypodermalia which do not always form a 

 quadrate lattice-work with their tangential rays, a large number of small dermal pen tacts 

 occur, with rough straight rays, of approximately equal length, and frequently somewhat 

 club-shaped at their extremities. The four tangentials intersecting at right angles are 

 often inclined slightly inwards. From the point of intersection a knob-like tubercle 

 sometimes projects outwards, representing the undeveloped external radial ray (PL LXI. 

 fig. 10) ; it is, however, generally absent. Between these dermal pentacts, perfectly 

 similar tetracts not unfrequently occur, in which the four rays, intersecting at right 

 angles, are usually curved shglitly inwards. 



In the gastral skeleton, as in Rhabdocalyptus, there are no large hypogastralia. The 

 autogastralia are all small rough pentacts, in which the straight rays are not club- 



