234 PERCY SLADEN TRUST EXPEDITION 



varying to more slender forms as shown In the figures, and even passing into the next 

 form. 



(7) Spined microrhabds (fig. 3 g). Slender ; covered with minute short spines ; 

 measuring about 0'022 by 0"002 mm. (exclusive of spines), but variable. This spicule is 

 extremely scarce in some specimens, though plentiful in others, so that it may very easily 

 be overlooked. It seems to be a characteristic feature of the genus Triptolemus and is 

 probably proper to Yodomia also. It may be a reduced streptaster. 



The condition of the material and the character of the skeleton make it impossible 

 to prepare satisfactory parafiin sections, but investigation by this method reveals the 

 presence of an enormously thick, gelatinous ectosome. This tissue appears to be of the 

 nature of that termed " chondren chyme " by SoUas [1888]. Imbedded in the clear, 

 gelatinous, faintly staining matrix are numerous oval, granular cells, about 0"02 mm. 

 in diameter, each with a small nucleus and each surrounded by a well-defined shrinkage 

 cavity or lacuna in the matrix, usually much larger than itself The relative proportion 

 of cells and matrix varies in diflPerent parts, but generally the cells lie pretty close 

 together. The outermost portion of the ectosome is occupied by the thick layer of oval 

 microrhabds. 



This species in many respects resembles Lebwohl's Yodomia ijimai from Japan, but 

 it differs in im2Dortant details of spiculation. Thus the mesotrisenes of Y. ijimai have 

 simple cladi while in Y. perfectus they are branched ; Y. perfectus has no long-shafted 

 triaenes and Y. ijim,ai appears to have none of the smooth oval microrhabds which are so 

 abundant in our species. 



Register Nos., Locality, &c. vi., ix. 1, x. 1, 2, 3, 4, all from Saya de Malha, 4.9.05, 

 C. 1, 150 fathoms. 



Family Stellettidse. 



Astrotetraxonida with long-shafted trisenes ; without calthrops, sterrasters and 

 aspidasters. (In a number of genera and species with reduced spiculation, constituting 

 the so-called family Epipolasidse, the tetract megascleres have completely disappeared, 

 while in certain forms the astrose microscleres seem to have vanished.) 



The original Stellettids appear to have arisen by the development of long-shafted 

 triajnes and the radial arrangement of the megascleres in some primitive pachastrellid 

 ancestor. It is a very remarkable and interesting fact that along a number of more or 

 less distinct lines of descent within the stellettid family the power to produce tetract 

 megascleres seems to have become exhausted and these lines have passed over into the 

 monaxonellid condition. It was for such lines that Sollas [1888] proposed the family 

 Epipolasidse, which he placed as an "Appendix" to his Astrophora Euastrosa ( = Stellettidse). 

 In the Epipolasidse he recognised three genera, Amphius, Asteropus and Coppatias. His 

 diagnosis of the family fully recognises the principle of the loss of tetract megascleres, 

 it runs as follows : — " Euastrosa (1) without trisenes, possessing oxeas and one or more 

 forms of aster. The oxeas arranged partly in radiating fibres, partly scattered loosely 



