22 C. F. JKXKIX. 



infrequently that spicules may be found with one of the paired rays pointing almost 

 radially inwards, and at first sight suggesting that sub-dermal triradiates are present 

 {cf. Fig. 59). The peculiar shape of the dermal triradiates, however, makes it ea.sy 

 to prove that it is always a paired ray, and not the basal ray, which is centripctally 

 directed. 



Dermatreton chartaceum. 

 (Plate XXVII., Fig. 5, and Plates XXXI. and XXXII., Figs. 59-04.) 



There is only one specimen of this new .species in the collection. It was found at 

 a depth of 180 fathoms. it is nearly straight, 2o mm. long x 3 mm. maxinuun 

 diameter, (juite white as preserved in alcohol, and has the appearance of a delicate paper 

 tul)e (.see Fig. 5). The walls are only 0";32 nun. thick at their thickest point. The 

 reticulated pattern on the surface is too small to be readily seen with the naked eye. 



The structure of the body wall is sliown in Fig. 59. The flagellated 

 chambers open directly into the gastral cavity through contractile apopyles (see 

 Fig. GO). The skeleton of the Hagellated chambers consists normally of a single 

 row of sub-gastral triradiates, l)ut there is occasionally a smaller triradiate half-way 

 between the gastral and dermal layers. There are also fine hair oxea, not shown in 

 the figure, surrounding the flagellated chambers. The distal ends of the flagellated 

 chamber skeletons are strengthened by oxea, which project a short distance beyond the 

 dermis. The distal ends of the chambers are covered by a reticulated cortex with a 

 skeleton formed of curved triradiates (see Fig. 63). 



The gastral skeleton (Fig. 62) is formed of large quadriradiates, among whicli 

 there are a very few which appear to have no apical ray. 



The o.scular skeleton is shown in Fio;. 61. The edge, which is .sliohtlv 

 everted, is formed of small quadriradiates. There is a very short fringe of hair oxea, 

 amongst which are a few stout oxea smiilar to those in the body wall. The dermal 

 triradiates extend up to tlie edge. 



Spicules (Fig. 64). 



Oxea. — There are two sorts of oxea : — 



(a) Projecting oxea, sbghtly crooked, slightly hastate, 130 m to 270// long 



X 11 // to IG/u thick. 

 (A) Hair oxea about 1 m thick. 



Irimdiates. — The triradiates are of two sorts : — 



(c) Mate sub-gastral triradiates forming the tubar skeleton. Basal ray straight, 

 tapering to a moderately sharp point, 320 /a to 700m long x 9m to 10m 

 thick. Paired rays nearly equal, slightly crooked, 100 m to 160 m long 

 X 9m to 12m thick, Iduntly pointed. Oral angle variable from 170° to 

 120°; strongly folded ; angle of fold 120° to 130°. 



