REPORT ON THE HEXACTINELLIDA. • 241 



slender umbel rays, wliicli vary considerably in length in different anipliidiscs, and are 

 often markedly divergent (PL XLII. fig. 3). The smaller and smallest amphidiscs, 

 varying from 0"04 to 0"02 mm. in length, bear short, approximately or perfectly 

 hemispherical terminal umbels, with eight, twelve, or more slender umbel rays (PL XLII. 

 figs. 4 and 5). 



The firm skin which lines the long cylindrical gastral cavity is supported by strong 

 smooth hypogastral pentacts, which entirely resemble the already described hypodermalia. 

 The bushy autogastral pentacts are also exactly similar to the autodermals. I did not 

 find here the largest form of amphidisc, with broad paddle-like or lancet-shaped umbel rays, 

 but the medium-sized and small forms were present in abundance, as in the skin. On the 

 internal surface of the numerous large ramified efferent ducts, which occur in the gastral 

 walls, hypocanalicular oxypentacts with canalicular pentact pinuli occur, but the latter 

 are different from the autodermal and autogastral forms in this, that their four, 

 sometimes smooth, sometimes spinose basal rays are on an average longer, and the freely 

 projecting ray less thickly beset with lateral curved spines (PL XLII, figs. 8, 9, 12, 13). 

 The further the efferent camd system is followed tow'ards the chamber parenchyma, the 

 less conspicuous, the more slender and sparse do the pinules become, and the weaker is 

 the development of the spines on the freely projecting ray (PL XLII. fig. 11) until tliey 

 finally disappear just before the orifices of the chambers. 



The spicules, which project radially in long tufts from the lateral surface, are diacts 

 or uncinates, either smooth or covered with barbs. The long bundles, projecting at the 

 lower end consist of spicules, which are smooth at the upper pointed end, while the lower 

 is beset with spines, bent obliquely upwards and outwards, and usually distinctly disposed 

 in two opposite rows. Somewhat above the extremity the spines disappear, and the 

 spicule ends in an anchor structure, which exhibits two, more or less long, sliglitly re- 

 curved, opposite teeth (PL XLII. fig. 7). Three such teeth exceptionally occur. If two 

 anchor teeth are formed, as is usually the case, they lie in the same plane as the 

 biseriate alternately disposed barbules of the shaft (PL XLII. fig. 7). 



2. Pheronema carpenteri (W^'ville Thomson) (PL XLIIL). 



On the "Lightning" Expedition in the north of Scotland, Wyville Thomson found, 

 at a depth of 530 fathoms, some beautiful sponges which he described and figured in 

 a masterly fashion^ under the title Holtenia carpenteri. Of these I obtained for examin- 

 ation some spirit and dried specimens captured by Wyville Thomson himself on the 

 "Lightning" and "Porcupine" Expeditions, and other specimens well-preserved in 

 alcohol, which were dredged by Mr. John Murray on the "Triton" Expedition. On 

 the Challenger Expedition several much torn portions of this Hexactinelhd were trawled on 



■ P7ii7. Trans., 1859, p. 701. 

 (zOdL. CHALL, EXP. — PART LIU. 1887.) Ggg 31 



