KEPORT ON THE HEXACTINELLIDA. 125 



(PI. XXIV. fig. 7) exactly like those which we have already noted iu Balanites. Simple 

 oxyhexasters also occur with short principal rays, and long, frequently somewhat rough, 

 terminals. The division of one or several principal rays often does not take place, so that, 

 as in PI. XXIV. fig. 8, some rays become divided into two or three terminal rays, while 

 others which remain undivided are straight and run out to a sharp point. 



Rosettes are represented only by the form figured in PL XXIV. figs. 4 and 6. Each 

 of the six smooth and moderately long principals passes into a narrow conical tuft of 

 eight or more almost similar, straight, fine terminal rays, each of which is somewhat rough 

 towards the extremity and is provided with a small, convex, marginally pronged, terminal 

 plate. Here and there, abnormally, one or other of the secondary rays does not occur on 

 the extremity of the principal ray but laterally, and is inserted more or less close to the 

 axial node as if it had moved down to this position. 



The pentact hypodernialia have a strong radial ray which is wholly or partially beset 

 with spines, while the four transverse rays which are spread out beneath the dermal 

 membrane but rarely exhibit small spines, and usually appear somewhat roughened on 

 their bluntly pointed extremities. 



The autodermalia are hcxact piuuli in which each of the freely projecting (usually 

 0'05 mm. long) distal rays resembles a crowded oval fir cone with a short smooth stalk 

 (PI. XXIV^. fig. 10), or is more rarely narrower and longer (PI. XXIV. fig. 2). 



The four slightly conical transverse rays lying in the dermal membrane, and the 

 somewhat shorter proximal ray, arc onl}^ beset with small prongs on the outer portion. 



While the hypogastralia do not difi"er essentially from the hypodernialia, the auto- 

 gastralia which project over the whole convex upper side of the body of the sponge difiier 

 essentially from the autodermalia, inasmuch as the freely projecting, and at the same 

 time distally directed ray, is very long (1 mm. or more), narrow, drawn out to a fine 

 point, and also beset with relatively short prongs (PL XXIV. fig. 5). On the other 

 hand, the ray directed towards the parenchyma is greatly reduced, or has entirely 

 disappeared, so that the majority of autogastralia no longer represent hexacts but 

 pentacts, in which the short, conical, ti'ansverse rays are beset with small prongs either 

 on the outer extremities alone or all over. 



The difference between the short crowded liexact autodermalia and the long pointed 

 pentact autogastralia is very clearly indicated on the outer margin of the disc where 

 both border on one another, yet it may also be readily recognised on the other side by 

 the shorter projecting distal ray and the short proximal ray of the outermost auto- 

 gastralia. Both are really but difterent members of the same series. 



It is noteworthy that in those autodermalia with a greatly prolonged distal ray, which 

 occur here and there between the short and crowded forms, the inner proximal ray is 

 usually absent (PL XXIV. fig. 3). 



In the parench}Tna of the stalk the principal hexacts are in the minority, and the 



