REPORT ON THE HEXACTINELLIDA. 37 



I liuvc applied the term " Uncinata " to the rod-like forms which run out to a point 

 at both ends, and are provided with barbs pointed in the same direction. For such forms 

 Carter^ has lately suggested the name " Barhula," Init this term would not be generally 

 imderstood. In some species these more or less thickly placed prongs lie close to the 

 body of the rod, while in others they are obliquely directed. They are sometimes delicate 

 and narrow, sometimes broad and scale-like. 



Certain Hexactinellidan families have typical and regular Uncinata, while in others 

 they are absent. They are usually directed at right angles to the surface, with their 

 external points in the skin (PI. LXXIV. fig. 1, PL LXXXIV. fig. 1) ; occasionally they lie 

 obliquely to the surface or quite irregularly (PI. LXXVIII. fig. 2 ; PL XCV. fig. 2). 



Among the asymmetrical diacts a form occurs in which one of the two rays bears 

 numerous obliquely and outwardly directed teeth or scales, whilst the other remains 

 smooth (PL XXX. fig. 7), or exhibits only small knobs (PL XL. fig. G). 



Feeble, irregular, undulating curvature is exhibited especially on the frequently 

 numerous tuft-like, long and filiform diacts (PL V. fig. 14). The simple arc-Hke form 

 occurs, on the other hand, in shorter and stronger diacts (PL III. fig. 21 ; PL LXII. 

 fig. 6 ; PL LXIII. fig. 4). A. spiral cork-screw-like form is illustrated by the diacts of 

 Hyalostylus dives, which are rough on one side (PL LXX. figs. 5, 8). More marked 

 curvature of both rays in the same plane is exhibited by small diacts in Holascus stellatus 

 (PL XIV. fig. 12). In other cases the rays are bent towards each other in a hook-like 

 fashion, but on opposite sides (PL XVI. figs. 5-7). 



MONACTS. 



While the derived nature of a monact spicule is in many cases determinable by the 

 presence of rudimentary abortive rays (PL LXV. fig. 8), or by the persistent intersection 

 of the corresponding axial canals at one end of the spicule; this becomes difficult when 

 neither rudiments of other rays, nor traces of their axial canals persist. The presence of 

 a knob or disc-like expansion at one end does not of itself determine the monact 

 character of the spicule in question, since, as we have seen in the anchor-shaped diacts, 

 the axial cross of the central canal, which is the decisive character, lies at some distance 

 from the thickened end, and may thus demonstrate the diact character of the simple 

 spicule. 



It seems to me, however, that those spicules, called by Carter " Clavulw," which run 

 to a point at one end, and bear a knob or terminal toothed umbel at the other 

 (PL LXXI.-LXXV.) as characteristically seen in the genus Farrea, are really monacts ; 

 although I have. Like 0. Schmidt, been unable to detect an axial canal in their terminal 

 umbel, or in the swollen portion l)elow. This opinion is, however, the more probable, 



' Ann. and Mag. Nat. Hist., 1885. 



