REPORT ON THE HEXACTINELLIDA. 215 



sponge is cup-shaped, more or less curved outwards laterally, and truncated transversely 

 or obliquely above. The superior terminal surface is sometimes almost flat, usually, 

 however, markedly concave, and always j^rovided with a sharp-angled projecting marginal 

 fringe, and with a central more or less markedly projecting cone. From the inferior 

 lateral portion of this central cone four radial longitudinal plates extend as septa through 

 the gastral cavity, broadening out laterally to unite with the thick body-wall. By these 

 four cruciately disposed septa, four cavities opening widely on the upper terminal surface 

 are enclosed, and these are continued laterally and inferiorly into the tree-like branched 

 system of efi'erent canals. The fine terminal canals extend to within a short distance 

 of the external skin, and there end blindly in those diverticula of the membrana 

 reticularis which are characteristic of the Hyalonematidse (PI. XXXVII. figs. 1-3 ; 

 PI. XXXVIII. fig. l). Close below the inconspicuous annular basal pad, surrounding 

 the upper portion of the long much twisted root-tuft, there is an incrustation of 

 Palythoa, which embraces in some forms only a small portion, and in others two-thirds or 

 more of the long tuft. 



The total length of the sponge varies between 18 and 50 cm., of which the body 

 itself occupies, on an average, from 5 to 8 cm. The maximum diameter sometimes occurs 

 just below the upper end, sometimes about the middle, and varies from 3 to 6 cm. The 

 average thickness of the basal tuft, just below the lower end of the body, is 3 to 4 mm. ; 

 further down, however, it becomes greater until the brush-like divergence of the spicules 

 begins. Apart from some circular apertures from 1 to 4 mm. in diameter, the superior 

 convex surface of the body and the whole surface of the freely projecting conus are seen to 

 be fairly smooth. On the other hand, the whole lateral surface distinctly exhibits, even to 

 the naked eye, the rectangular lattice-work of the dermal membrane (PI. XXXVII. fig. 3). 



The parenchyma contains a few medium-sized superficially smooth oxyhexacts, and 

 numerous oxydiacts, disposed in strands or lying singly, with or without central swellings 

 or with two or four cruciate nodes (PI. XXXVIII. fig. 3). The small oxyhexacts 

 which occur in great abundance are all rough, and almost thorny, and have more or less 

 markedly curved rays (PI. XXXVIII. fig. 5). Isolated very small but strongly developed 

 oxyhexacts, with distally directed teeth (PI. XXXVIII. fig. 4), occasionally occur. 



The dermal skeleton, which appears on surface view as a conspicuous rectangular lattice- 

 work (PI. XXXVIII. fig. 2), consists of simple smooth medium-sized hjrpodermal oxypen- 

 tacts, and of abundant autodermal pentact pinuh, about 0'2 mm in length, with strongly 

 developed short-toothed basal rays, and somewhat strongly developed distal ra}^ with 

 short obliquely inserted, spines (PI. XXXVIII. fig 10), and finally of irregularly scattered, 

 large, medium-sized, and small amphidiscs. The former, measuring from 0'15 to 0'17 mm. 

 in length, have a strong knotted axial rod, and broad umbels with eight paddle- 

 shaped rays (PI. XXXVIII. fig. 7) ; the middle-sized forms have from ten to twelve long 

 narrow umbel rays (PI. XXXVIII. fig. 6) ; while the very abundant small forms bear 



