TETRAXONIDA. 45 



evident from the fact that the axial canal can be seen traversing the granular 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 130 fins. 



FAMILY HAPLOSCLERIDAE TOPSENT. 

 SUB-FAMILY GELL1INAE RIDLEY AND DENDY. 



GELLIUS RUDIS. 



(Plate XVII., figs. 1, IA, and Plate XXIV., fig. i a -l>.) 

 r.HiL'. 6V/////S null's, Topsent (29. p. 14, PI. I., fig. 0, and PI. III., fig. 4). 



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

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

 them of large size ; accordingly 1 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. massa R. and D. (15. plate III., fig. 6).* 

 The other specimens are in the form of thick sub-cylindrical unbrauched 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 oseules about 7 mm. in diameter with circular 

 raised rims. 



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

 smooth ; though, where the dermis is rubbed off, 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 M long, 19 - 4^ broad, and '8 /u thick, 



* In this variety the skeletal arrangement is very similar to that found in Gelliiis ntdis; the terminal 

 branehlets of the main fibres arc spread out beneath the dermal layer, and anastomose with branehlets from 

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

 the paniculate ends of the main fibres (as in G. rutlis), 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 dcniial 

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

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

 state that the 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 wt-11 a-; by oxeas from the subdermal 

 reticulum. The spicules of P. similis var. massa resemble those of G. rutlis in shape, but are smaller t\i/. '2'.K> x 

 9 - 75 p.). Accordingly P. similis var. massa is closely similar to G. rutlis in form, in skeletal arrangement, and 

 in spiculation ; in fact it very probably represents an example of a GiUiiix 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 with microscleres. Further, an instance of this kind furnishes some support to 

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

 Halichondrina. 



