378 HYALONEMA (SKIANEMA) AEQUATORIALE. 



Foreign skeletal elements are always met in the deep-sea hexactinellids 

 which have, like the specimen here described, been somewhat injured in capture. 

 I do not remember, however, ever having seen a sponge so rich in foreign spicules 

 as this one. The spicules in question could be determined as foreign because 

 they are identical with the pentactines, pinules, hexasters, amphidiscs, etc., 

 of Holascella euonyx, Hyalonema (Hyalonema) agassizi, Hyalonema (Prionema) 

 fimbriatum, Hyalonema (Phialonenia) pateriferum, and Hyalonema {Prionema) 

 spinosum brought up in the same haul together with the sponge here under 

 discussion. 



The dermal pinules (Plate 99, figs. 29-31) are generally pentactine, rarely 

 hexactine. The distal ray is straight, 200-260 n long, and 5-8 ^ thick at the 

 base. It ends in a rather slender sharp-pointed terminal cone, and bears every- 

 where, except at the base and at the tip, rather slender straight or slightly curved 

 spines, which are all strongly inclined towards its tip. The maximum thickness 

 of the distal ray, together with the spines, is 25-42 yu. The lateral rays are 

 cylindroconical, pointed, spiny, and 30-45 ix long. The proximal ray of the rare 

 hexactine forms (Plate 99, fig. 29) is 9-42 ^ long. 



The gastral pinules (Plate 99, figs. 25-28, 30) are a little larger than the 

 dermals and appear always to be pentactine. Their straight distal ray is 212- 

 275 M long, and 6-9 m thick at the base. It ends with a long and slender sharp- 

 pointed terminal cone and bears everjrwhere, except at the tip and at the base, 

 remarkably sparse spines. These spines are long, slender, straight or slightly 

 cur\'ed, and strongly inclined towards the tip of the ray. The maximum thick- 

 ness of the distal ray, together with the si:)ines, is 23-39 m- The lateral rays 

 are 35-48 m long and, like those of the dermal pinules, cylindroconical and 

 spined. 



The hypodcrmal and hypogastral penlactines seem to be quite similar. Their 

 rays are conical, straight, and blunt. The proximal ray is geneially 0.4-1 mm. 

 long, and 10-50 n. thick at the base. The lateral rays are 140-800 /j. 



The hexactine megascleres are mostly 360-850 /u in diameter, and have coni- 

 cal, blunt, and straight rays 9-31 n thick at the base. A few fragments observed 

 in the preparations indicate that some of these spicules attain a larger size. 



The ordinary superficial and choanosomal amphioxes are straight or slightly 

 curved and usually more or less centrotyle. In some no trace of a central 

 thickening could be made out. These spicules are 0.25 ^-1-9 mm. long, and 

 7-20 n thick near the middle. The central tyle is sometimes 6 /i in transverse 

 diameter, usually about 0.3 m more than the adjacent parts of the spicule. The 



