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



The principal supporting spicules of the loose parenchyma consist of large or 

 medium sized smooth oxyhexacts, with straight rays, and of straight or slightly curved 

 oxydiacts, which are roughened towards their conically pointed extremities, and exhibit 

 at their middle point four cruciate transverse tubercles, or an annular swelling, or 

 at least the intersection of axial canals. These oxydiacts either lie isolated, or are 

 for the most part disposed parallel to the surface. The larger and stouter forms 

 are usually accompanied and ensheathed by a number of long thin oxydiacts or comitalia. 

 As to smaller spicules, the parenchyma includes numerous regular oxyhexacts with more 

 or less roughened rays, and also a large number of oxyhexaster forms which are very 

 characteristic of this genus. In these the principal rays are comparatively long, simply 

 cylindrical, or narrowed in a slightly conical fashion, and are always somewhat roughened 

 terminally, where they divide into two or three short, diverging, conical terminals 

 (PI. LIV. fig. 5). When only two terminal rays are developed at the end of the 

 principal, the planes of forking of the two rays in the same axis of the spicule are at 

 right angles to one another. Finally, the parenchyma contains peculiar rosette forms, 

 occurring in regular, but not very abundant distribution. These belong to the ph;mi- 

 come type, but are not so minute as those of Lanuginella puj^ct. They attain to about 

 the same diameter as the above-described oxyhexasters, namely, about O'l mm. The 

 short, cylindrical princi]:)al rays bear terminally a plano-convex transverse disc, from the 

 outer convex surface of which several concentric whorls of S-shaped terminal I'ays arise. 

 These go to form a perianth-like form with several whorls, enclosing a central funnel- 

 shaped space (PI. LIV. figs. 4, 6). The thi'nnest portion of these delicate S-shaped 

 terminals lies near their origin, while the outer end becomes thickened in a somewhat 

 club-shaped fashion, exhibiting, however, a slight attenuation at the extremity. 



The dermal skeleton consists especially of hypodermal oxypentacts of variable size, 

 in which the long proximal ray is always straight and radially disposed, while the 

 four tangentials which go to form a quadrate lattice-work are usually curved gently 

 inwards. Like the proximal ray, the tangentials frequently appear to be roughened 

 near their conical extremities. Between these substantial pentact hypodermalia, the 

 dermal membrane includes small cruciate autodermal tetracts in great abundance and 

 in rectangular distribution. In these, the rough cylindrical rays, which are rounded off' 

 or even truncated at their ends, are curved slightly inwards, so that the whole spicule 

 appears to be uniformly arched with the convexity outwards (PI. LIV. figs. 2, 7). Some- 

 times, at the point of intersection of the four arms, an inward projecting boss or 

 tubercle persists as an indication of the undeveloped fifth (proximal) ray. In a few of 

 these dei-malia, the fifth ray is actually developed, and exactly resembles the 

 tangentials. 



The gastral skeleton differs strikingly from the dermal. The hypogastral pen- 

 tacts, as we should naturally expect, are wholly absent. Instead of them, there are 



