452 JAJNE STEPHENS: ATLANTIC SPONGES 



of the ridge. They are 2-6 mm. in diameter. The dermal membrane is very thin 

 and transparent. The consistence is very firm but compressible, the stalk being- 

 much more rigid than the upper part of the sponge. Colour in spirit pale yellow. 



The small specimen (PL XXXIX, fig. 4) is similar to the above in general outline, but 

 it only reaches a height of 70 mm., with a greatest breadth of 28 mm., and a thickness 

 of 10 mm. The stalk is 5 mm. in diameter and rises from a broad flattened base. 

 The oscula are confined to the upper margin of the sponge. The whole surface, 

 including that of the stalk and of the flattened base, is hispid with the projecting 

 ends of the main skeletal fibres. The hispidity is rather less marked towards the 

 lower part of the sponge than towards its summit. The texture, especially that of 

 the stalk, is much less firm than in the large specimen. Growing round the base 

 of the stalk are very small specimens of Pocillon hyndmani (Bowerbank), Myxilla 

 simplex (Baer), and Esperiopsis informis n. sp. 



The main skeleton is made up of a reticulation of strong fibres, as described by 

 Ehlers (6) for the type-specimen. The principal fibres run upwards through the 

 stalk and through the main body of the sponge. They branch, and bending towards 

 the surface, they pierce the dermal membrane and project beyond it to a distance of 

 about 2 mm. as strong tufts of spicules. They consist of a core of multiserially 

 arranged oxea surrounded by a thick sheath of spongin, and are about 0*15-0*25 mm. 

 in diameter. They are connected by a rather irregular network of more slender 

 fibres, the thicker of which consist of multiserially arranged oxea surrounded by 

 a strong spongin sheath. They are about 0*12-0*2 mm. in diameter. The fibres 

 are rather more closely placed in the stalk, thus giving a greater rigidity to it. 

 There is no special dermal skeleton. 



Spicules. — (l) Oxea, curved, tapering evenly to sharply pointed ends. They 

 do not vary much in size, being usually between 0'4-0"5 mm. in length by 

 0'02-0'024 mm. in thickness. (2) Isochelse palmatse. — These occur in great 

 abundance through the sponge and in the dermal membrane. They are 0*027-0*032 

 mm. in length. In some the peculiar bending inwards of the axis from the inner 

 side of the tooth, which is characteristic of many Homceodictya species, can be 

 clearly seen, both in side view, and, showing as a tubercle, in front view. In other 

 isochelse the structure is not so well marked, and in many it cannot be made out 

 at all. The spicules of the small specimen agree exactly with those of the large 

 specimen, there being, however, a larger proportion of more slender oxea present. 



As far as can be made out from the fragment of the type-specimen available, 

 the arrangement of the skeleton agrees exactly with that of the Scotia specimens, 

 and the spicules are identical in size and shape. Ehlers (6) gives 0*44 mm. 

 for the length of the oxea in Esper's specimen, and this is about the average length 

 of the oxea in both the large specimens, but in the type, as in the recently collected 

 specimen, they vary between 0*4-0*5 mm. in length, and between 0*02-0*024 mm. 

 in thickness. 



