DENDY— REPORT ON THE HEXACTINELLID SPONGES (TRIAXONIDA) 213 



The skeletal framework (fig. 2) consists of a very lax reticulation of large, smooth 

 hexacts, with very long, slightly curving rays soldered together and joined by synapticula 

 in a most irregular, but often ladder-like, fashion. A characteristic feature of this frame- 

 work is that it sends out free ends, which project into the gastral cavity in the form of 

 large hooks with very varying degrees of curvature (fig. 3). 



The following kinds of separate spicules occur in the sponge : — 



(1) Large and small parenchymal hexacts, having straight, slender rays with slightly 

 roughened ends (figs. 4, 5). 



(2) Large dermal and gastral pentacts ; rays slightly roughened at the ends 



(%• 6). _ 



(3) Occasional small pentacts, with knob-like vestige of the sixth ray ; rays slightly 



roughened (fig. 7). 



(4) Discohexasters, varying somewhat as regards the curvature and arrangement of 

 the terminal rays, which end in small discs with toothed margins (figs. 8, 9). 



(5) Large hexasters with terminal rays ending in small knobs, and provided with 

 rather long, backwardly pointing spines, the most distal of which may arise in a whorl 

 from the terminal knob. These spines are very easily broken off", and this has evidently 

 been the case to a large extent in the specimen figured (fig. 10). It is very difficult to 

 find a specimen of this spicule perfect enough to draw, though a fair number of them 

 occur in my preparations. 



The only other species of Aulocalyx hitherto described is Schulze's A. irregularis, 

 the type of the genus. To judge from the description and figures given in the 

 "Challenger" report the chief difference between the two lies in the external form. In 

 the "Challenger" species "the general form was that of a broadly expanded cup with 

 complex, much folded or diverticulated wall." The generic diagnosis mentions the occurrence 

 of " short laterally projecting tubes." These are not mentioned in the specific description 

 but the general form is compared to that of Periphragella elisce, the figure of which 

 (PL LXXX) shows numerous short tubular projections, with open mouths, scattered 

 irregularly over the outer surface of the cup. Schulze's general figui'e of the external 

 form of A. irregularis (PL LX, fig. 1) does not show any distinct lateral tubes, but the 

 specimen was evidently much injured. He gives a separate figure (fig. 2), however, 

 of the macerated skeleton of a lateral tube, which seems to show that these structures 

 are of the same nature as the tubular openings in A. serialis. There is no indication, 

 however, that they are arranged in longitudinal rows as in the latter species, and the 

 form of the cup in the two cases appears to be quite different, being very much narrower 

 in A. serialis. 



Another difference is found in the shape and size of the large, spiny-rayed hexasters 

 or rosettes. Those of A. serialis are only about 0"24 mm. in diameter, while those of 

 A. irregularis measure about 0*4 mm. Moreover, in the latter the ends of the long 

 terminal rays are " simply convex, or more rarely somewhat knobbed," while in A. serialis 

 they are, usually at any rate, distinctly knobbed, with a terminal whorl of backwardly 

 pointing spines coming off" from the knob as shown in fig. 10 a. 



How far the differences between the two forms can be regarded as really specific 



