ABT. 12 HEXACTINELLID SPONGES — OKADA 89 



all small in the upper part of the gastral cavity. Lower down, larger 

 ones become interspersed. The openings of all are covered by the 

 sievelike layer of the gastral skeleton. 



Spicidation.. — The parenchymalia are all slender diactins either in 

 a loose feltlike arrangement or grouped together into moderately 

 thick, ill-defined bundles. The principal may attain a length of 6 

 mm or more and a breadth of 52/x at the middle ; it tapers gradually 

 toward both ends, which are rough and conically pointed. All sizes 

 down to comitalia only 12/^ in thickness are to be found. All the 

 smaller diactins have roughened ends, which taper very slightly to 

 a conical tip, measuring S^a broad. 



The hj^podermalia and hypogastralia are likewise diactins; pent- 

 actins are not present. They are generally 20ju, in breadth and less 

 than 1.5 mm in length. They quite agree in appearance with similar- 

 sized parenchymalia, except in the fact that the spicular center is 

 often, but not always, externally marked by an inconspicuous annular 

 swelling. 



The dermalia are hexactinic pinnies, so far as those of the body 

 proper are concerned. The pinular distal ray as a wdiole is spindle- 

 shaped; it is 110/x to 160/A long and 14/^ to lS;a broad in the middle, 

 which is about the broadest part. In this part the obliquely up- 

 wardly directed, elongate, conical spines may be as long as 8/i. 

 The rhachis is smooth for a short distance at the base, which is about 

 8/A thick; its conically pointed, outer end forms the tip of the pinular 

 ray. The remaining five rays are somewhat slender and bluntly 

 pointed at the end. They are beset with small, usually erect prickles, 

 sparingly at the base but more pronounced at the end ; length, IIO/a 

 to 120)U. The proximal ray is usually slightly shorter than the 

 paratangentials of the same pinule, measuring 105/a to 130/* in length. 

 The fine quadratic-meshed dermal latticework is formed by two to 

 six paratangentials of two to six adjoining pinnies lying side by 

 side for nearly their entire length. Here and there, among the der- 

 malia, I have found such forms as may appropriately be regarded 

 as early stages in their development. They are much smaller, 

 slender-rayed hexactins, in which either there is no distally directed 

 ray or it is but little differentiated from the other rays, being nearly 

 as prickly as these. 



The gastralia are pinularlike hexactins. The free ray is much 

 longer, 260/i to 300^ long and 8/* to 12/* broad at the base, beset with 

 strong prickles, which are projected obliquely upward and pro- 

 nounced at the extremity. The remaining five rays are all slenderer 

 and gradually taper toward the conically or sharply pointed end. 

 But frequently one of the paratangentials shows a somewhat pinular- 

 like appearance and is provided with strong prickles at the end. 



