EEPORT ON THE HEXACTINELLIDA. 95 



and synapticula (PL VIII. fig. G), into a continuous network, which seems to be firmest 

 on the inferior portion of the sack, becoming more and more loose towards the upper 

 end. AYhile the principal strands of fibres are irregularly disposed, for the most part 

 obliquely, on the inferior and middle thirds of the body, the upper third exhibits a more 

 regular arrangement of the longitudinal beams and circular transverse ridges. 



The latter lie, as in all Euplectellidaj, on the inner side of the former. The strong 

 principalia of the lattice-work are in the regular upper portion almost exclusively 

 tetracts, in the larger and uu)i\' irregular inferior portion, on the other hand, triacts and 

 diacts predominate. The comitalia consist chiefly of triacts and diacts. 



Closely disposed spicules, with from six to two rays, also occur in the parenchyma, 

 viz., somewhat numerous, small, smooth or spinose, regular hexacts, with rays running 

 out to fine points (PL XL fig. 2); more rarely small, smooth discoh exacts (0"17 mm. in 

 diameter), with from four to six hooks on the arched terminal discs, and finally, disco- 

 hexasters irregularly scattered in somewhat large numbers (PL XL fig. 1; PL VIII. fig. 4). 

 ]\Iost of these discohexasters exhibit the same characters and dimensions as the discohexacts, 

 which have just been mentioned. The very short principal rays usually run out into two, 

 less frequently into three, long terminal rays, which are, at their origin, united in a bow- 

 like manner, and which, narrowing in the middle, again increase in strength towards the 

 terminal hemispherical disc, which bears six strong hooks (PL VIII. fig. 4). Hexasters 

 with somewhat longer and narrower terminal rays occur scattered at intervals, and on 

 their transversely truncated extremities, four to six small hooks project transversely. 

 In the neighbourhood of the outer surface graphiohexasters occur with long tufts of 

 parallel, straight, very delicate, terminal rays (PL VIII. fig. 5). 



The sword-like hexact hypodermalia are delicate, and run out to fine points. To their 

 distal ray a floricome is always attached, which does not differ essentially from the well- 

 known floricome of Euplectella asj^ergiUum (PL VIII. fig. 3). 



The gastral skeleton consists of somewhat stronger pentacts, in which both the 

 prolonged distal and the four tangentials are either transversely rounded ofi", or terminate 

 in a knob-like swelling (PL VIII. fig. 7). 



The thickened margin which surrounds the upper terminal opening bears two circularly 

 arranged rows of hexacts with strongly developed distal rays. In the spicules of the 

 outer circle the straight distals, which measure from 2 to 3 mm. in length, are directed 

 obliquely outwards and upwards, while the slightly lient, strong, distal rays of the inner 

 circle, which are 1^ cm. in length, bend together in dome-like fashion over the opening, 

 so that only a central space, about 8 mm. in breadth, remains (PL VII.). 



The folded layer of simple sacciform chambers surrounds clefts or short canals, which 

 either open freely by wide internal openings, or are arched over by a continuation of 

 the gastral skin (PL XL fig. 1). The inner trabecular framework occurs in a thin layer 

 on the inner side of the eff'erent passages which lead from the wide openings of the 



