REPORT ON THE HEXACTINELLIDA. 249 



aud felted, is difficult to estimate. In the largest forms it cannot be less than 10 

 to 20 cm. 



The concave internal surface of the upper gastral cavity exhibits a tolerably firm and 

 solid portion, about 10 mm. in breadth, and arched slightly inwards, while aU the rest of 

 the surface forms a tolerably well-differentiated quadratic lattice-work, the strands of 

 which enclose meshes, 2 mm. or less in width. 



From this description, and from the figure in PI. XLIV. fig. 1, drawn from a 

 photograph, the external specific differences between Pheronema globosum and Pheronema 

 hemisphsericum, Gray, must be evident enough. As to parenchymal spicules, mention 

 must be made of (1) the numerous rather large oxyhexacts, with long, straight, or slightly 

 curved smooth rays, which are sometimes reduced in number so as to result in pentacts, 

 tetracts, or triacts ; (2) medium-sized smooth oxydiacts, which are for the most part 

 somewhat bent ; (3) long radial uncinates, reaching as far as the surface or even further ; 

 (4) very numerous short uncinates, which though especially abundant round about the 

 efferent canals, occur in varied disposition, and are distinguishable from the long uncinates 

 not only by their smaller size, but also by this, that the strong laterally inserted spines 

 are curved, and somewhat markedly divergent ; (5) slender oxydiacts of rarer occurrence, 

 with strongly developed, or almost wholly reduced spines (PI. XLIV. figs. 4, 7). 



The numerous medium-sized and small amphidiscs (PI. XLIV. fig. 3) which occur in 

 the parenchyma, do not, in my opinion, really belong to it, but owe their origin to the 

 outer skin, or to the membrane of the gastral or canalicular cavities, whence they have 

 been forcibly pushed or floated into the parenchyma. 



The dermal skeleton includes strong hypodermal oxypentacts with long, smooth, 

 straight or slightly bent rays, measuring 10 mm. or more in length (PI. XLIV. figs. 8, 9). 

 The four tangential rays are inclined slightly inwards (PI. XLIV. fig. 9). Numerous 

 strongly developed autodermal pentact pinuli also occur, exhibiting a somewhat thick, 

 bushy, free distal ray, thickly beset with strong, bent, lateral spines, and four moderately 

 long, blunted basals, slightl}^ inclined inwards, and thickly beset with short spines, 

 (PI. XLIV. figs. 3, 5). In various places the distal ray of the pinuli is somewhat more 

 slender, of greater length, and slightly curved. 



As to amphidiscs, I observe a large form, 0"2 mm. long, with campanulate but 

 rather short terminal umbels, in which the eight, or more rarely six, umbel rays are 

 tolerably smooth, and moderately rounded in paddle-like fashion (PI. XLIV. fig. 6). 

 The rather thick stalk is richly beset with roundish tubercles. Besides these, somewhat 

 small amphidiscs occur, with exactly similar form, and finally very small forms, 0'02 mm. 

 or less in length (PI. XLIV. figs. 12, 13). 



The dermal skeleton of the gastral cavity resembles that of the outer skin, except in 

 this, that the pinules are furnished with a much longer and more slender distal ray. 



The pleural prostalia consist of the long, more or less markedly projecting uncinates, 



(ZOOL. CHALL. EXP. — PART LIII. — 1887.) Ggg 32 



