BY E. F. HALLMANX. 



from tlie oseula. The dermal mem- 

 brane varies from 5U to over 1 00 (rarely 

 to 130/x) ill thickness, and is closely 

 packed throughout with sjuruUe. 



The distinctive internal features are 

 the very much greater relative develop- 

 ment of the axial f une as compared with 

 the extra axial skeleton, the slightly 

 stouter and more spoiiginous fibres, and 

 the greater dimensions of the mega- 

 scleres. In the first-mentioned respect, 

 as n+ay be seen from the figure(Pl. xxv., 

 fig. 2), the skeleton (which is of a pale 

 brownish-grey tint) a})[)roaches rather 

 closely to that of T. sr<ibrosns — inas- 

 much as, throughout the greater part 

 of the length of the branches, the axial 

 condensation occupies not less than 

 three-fourths of their diameter; only 

 towards the extremities of the branches 

 do the radial fibres become distinctly 

 apparent, and even there their length 

 never much exceeds 1mm. The diam- 

 eter of the radial fibres varies from 30 

 to ovei' 80 /x, and their spicules are 

 always surrounded by a well-defined, 

 though usually very thin layer of 

 spongin. The spongiii does not extend 

 to the very extremities of the fibres, 

 but terminates quite abruptly a short 

 distance therefrom, leaving the ciul- 

 most spicules free. 



In correspondence with their greater 

 stoutness, the megascleres (c/". Text-figs. 

 4 and 5) are slightly more fusiform than 

 in the typical variety; and their apices 



Text-lig.5. — Trachycladas digi/atus var. gracilis. Me^asclciL's : a, horn 

 the stalk; /', fium the branches. 



