TETRAXONIDA. 45 



evident from the fact that the axial canal can be seen traversing the oranular zone 

 Some of the exotyles have one or more swellings in the length of the shaft. 



The single example was dredged near Winter Quarters, at No. 6 hole, in 1.30 fms. 



Family HAPLOSCLERIDAE Topsent. 



Sub-Family GELLIINAE Ridley and Dendy. 



Gellius rudis. 



(Plate XVII., figs. 1, 1a, and Plato XXIV., fig. 1 a-h.) 



1002. GelUii:< rwlis, Topsent (29. p. U, PI. I., fig. 0, and PI. III., fig. 4). 



The type of this species, described by Topsent, was a small gloliular specimen 

 "27 mm. in diameter. The present collection contains six pieces of this sponge, some of 

 them of large size ; accordingly I am enabled to slightly supplement the original 

 description. The largest fragment, 18 x 5 x 2"5 cm. in dimensions, is massively 

 lobate and closely resembles Petrosia similis var. mas.m R. and D. (15. plate III., fig. 6).* 

 The other specimens are in the form of thick sub-cylindrical unbranched or branched 

 fragments, the largest (PI. XVII., fig. 1) being 14 cm. in length and 2-5 cm. in 

 diameter. Several of the pieces have oscules about 7 mm. in diameter with circular 

 raised rims. 



The surhice, where the dermal membrane is intact, is to the naked eye quite 

 smooth ; though, where the dermis is rubbed oft", the surface appears very finely hispid 

 as Topsent describes, and feels rough to the touch. 



A vertical section of a branch in the plane of the axis shows main longitudinal 

 lines of fibres curving outwards from the axis to the surface as they pass upwards, and 

 dividing in a more or less paniculate fashion near the surface ; the secondary fibres, one 

 or two spicules thick in the centre of the specimen, become much thicker a little below 

 the dermal membrane. 



The oxeas (XXIV. la), 403 x 20 m, are sub-tornote. The C-shaped sigmata have 

 a uniform curve almost in one plane ; they are 37 /j- long, 19 "4 m broad, and '8 m thick, 



* In this variety the skeletal an'angement is very similar to that found in Gellius rudis; the terminal 

 branchlets of the main fibres are spread out beneath the dermal layer, and anastomose with branchlets from 

 neighbouring main fibres ; this sub-dermal reticulum, then, is due solely to the spreading out of the periphery of 

 the paniculate ends of tlic main fibres (as in O. rudis), and is not as one might at first suppose a special dermal 

 skeleton ; the central tufts of the main fibres proceed vertically up to the surface ; also, not a few scattered oxeas 

 pass obliquely or vertically upwards from the subdermal network of spicule fibres ; accordingly the dermal 

 membrane is to a great extent supported on tlie tips of vertical oxeas. Though Ridley and Dendy clearly saw that 

 tlie dermal reticulation was only the uppermost layer of the main skeleton (15. p. 11), it was not quite correct to 

 state tliat tlie dermal membrane was not supported on tufts of spicules; a vertical section shows that it is sup- 

 ported in this manner, viz., by the central tufts of all the main fibres, as well as by oxeas from tlie subdermal 

 reticulum. The spicules of P. similis var. massa resemble those of G. rudis in shape, but are smaller (viz. 239 x 

 9 '75 fj.). Accordingly P. similis var. massa is closely similar to O. rudis in form, in skeletal arrangement, and 

 in spiculation ; in fact it very probably represents an example of a Gellius which has lost its sigmata. I have 

 gone into this matter in some detail because it is always interesting to trace the probable line of descent of a 

 Renierine sponge from some form witli microscleres. Further, an instance of this kind furnishes some support to 

 part of Dendy's recent scheme of classification, viz., that of making the Gelliiuae the starting-point of the 

 Halicliondrina. 



