REPORT ON THE HEXACTINELLIDA. 311 



ruptioii over the whole outer surface of the sponge, and extends over the external 

 openings of all the prismatic mesh-spaces. In like manner the gastral membrane, which 

 has a perfectly similar structure, extends internally parallel to the former, and covers 

 the inner openings of the prismatic honeycomb-like meshes. Between the two 

 perforated bounding membranes a fine skin extends deeply folded in funnel-shaped 

 fashion; this forms a continuation of the wall of the chambers, which are shaped 

 like the finger of a glove, and lie around and open into the common central space. The 

 latter is provided with an internal large exhalent orifice. This remarkable funnel-shaped 

 expansion of the chamber wall may be supposed to have arisen by amalgamation of 

 some specially large external chambers whose dividing walls projected to some extent 

 even into the excurrent central space (PL LXXXIV. fig. 1 ; PI. LXXXVI. fig. 2). 



The dermal skeleton consists of hexacts, in which each of the projecting outer rays 

 has usually a tree-like appearance, though sometimes reduced to a prickly peg or knob, or 

 even in many cases to a small tubercle, so that finally the spicule in question is no longer 

 to be regarded as h exact but as pentact. Besides these dermal hexacts or pentacts 

 scopulse with knobbed or pointed terminal rays also occur. 



The gastral skeleton consists of diacts which are completely enclosed in the gastral 

 membrane. 



Among the loose parenchymalia, there are present in addition to the uncinates which 

 project at right angles to the outer surface, small hexacts and hexasters of various kinds, 

 in variable abundance and irregular distribution. 



It is doubtful whether Aphrocallistes hcatrix, Gray, and Aphrocallistes bocagei, 

 Wright, are distinguished by suificiently marked and sufiiciently constant peculiarities to 

 be regarded as distinct species. On the other hand, the new forms which, on account of 

 their figure, I have named Aphrocallistes vastus and Aphrocallistes tubulosus, I regard 

 as sharply defined " good species. " 



1. Aphrocallistes heatrix. Gray (PI. LXXXIV. figs. 9, 10). 



Since I had an opportunity of examining in the British Museum the original specimen 

 from Malacca on which this species was established by Gray in 1858, I can, in the first 

 place, bear testimony to the correctness of Gray's description and figures of the micro- 

 scopic structure, and can also confirm those of Wjrville Thomson, Bowerbank, and Carter, 

 in regard to the minute structure of the dietyonal framework and the isolated spicules. 

 I may, therefore, refer the reader to these representations. 



Among the comparatively insignificant, and hardly qualitative distinctions which 

 have been noted in regard to the microscopic structure of this form as compared with 

 that first described by Perceval Wright (in 1870) from the Atlantic basin, special 

 emphasis is laid on a spicular form which has been spoken of by aU observers since Wyville 



