446 JANE STEPHENS : ATLANTIC SPONGES 



The sponge forms a thick encrustation. The upper surface rises in a number 

 of parallel-walled meandrine ridges, about 3-6 mm. in height and 2-3 mm. apart. 

 The summits of the ridges are slightly hispid. 



The dermal membrane is thin and easily detachable. No oscula or pores could 

 be made out. The consistence is firm, but compressible. 



The colour in spirit is pale yellow. 



The largest of the three pieces in the collection is 65 mm. by 55 mm., with 

 a thickness of about 35 mm. 



The main skeleton is made up of a reticulation of well-developed fibres, in which 

 a good deal of spongin is present. The principal fibres run upwards through the 

 sponge. They branch, and reaching the surface of the sponge their terminal 

 spicules pierce the dermis and project slightly. They contain a core of multiserially 

 arranged spicules, consisting chiefly of large skeletal styli, but often containing 

 in addition slender styli similar to those of the dermis, short acanthostyli, and 

 bundles of long, rhaphide-like toxa, all being enveloped in a distinct sheath of 

 spongin. The main fibres are echinated by numerous short acanthostyli. They 

 are about 0'06-0'13 mm. in thickness and lie about 0'15-0'3 mm. apart. 



The connecting fibres vary in diameter from 0'025-0'05 mm., and do not, 

 as a rule, contain spicules. Sometimes one large stylus is present enclosed in 

 spongin, or, more rarely, two styli lie side by side. 



The dermal skeleton is made up of slender styli, lying tangentially in the 

 dermal membrane. In places the styli occur singly, but they are usually crowded 

 together into flat bundles lying tangentially, or projecting more or less obliquely 

 beyond the surface of the sponge. There are, however, no closely set vertical 

 bundles of dermal spicules such as are characteristic of the species separated by 

 some authors from Clathria and placed under the genus Rhaphidophlus. The 

 hispidation of the surface is caused chiefly by the projection through the dermis 

 of the spicules at the ends of the main fibres. 



Spicules. — (l) Large styli coring the fibres. — The shaft is a little curved and 

 tapers evenly to a sharp point, or there is occasionally a very slight constriction 

 above the head. The spicule is sometimes smooth, but there are usually very 

 minute spines on the head, or there are fewer stronger spines instead of the more 

 numerous slender ones. Length '23-0 "45 mm., with a maximum diameter of 

 0'021 mm. (2) Acanthostyli echinating the fibres. — The shaft is straight and 

 strongly spined along its whole length, the spines on the shaft being curved, 

 with their points directed downwards. Length 0' 12-0' 15 mm. by '01-0 '01 4 mm. 

 (3) Dermal styli. — Straight, minutely spined on the head, usually between 0'14 

 and 0'3 mm. in length by 0'005-0'008 mm. (4) Isochelse palmatse. — Present in great 

 numbers throughout the sponge and in the dermal membrane. Length '01 5-0 '02 

 mm. (5) Toxa. — These occur in abundance, singly, or in rhaphide-like bundles, 

 through the sponge and in the dermal member. The length is very varying, from 



