REPORT ON THE HEXACTINELLIDA. 31 



pointed, outwardly directed, and divergent terminals. Such forms I have designated 

 " o.ryhexasters." All the six principal rays are usually divided into an equal numljcr 

 (two to five or more) of terminals, but the number of the latter may vary in tlie dilierent 

 principals even in one and the same oxyhexaster ; and it may even happen that indivi- 

 dual principals remain undivided. In the extreme case (PI. LVI. fig. 8), only one of the 

 six principals is forked, while the other five run out to simple points. It is noteworthy 

 that, in a division of a principal ray, the divisional planes of the two principals which are 

 directly opposite to one another, and therefore belong to one axis are mutually disposed 

 at right angles (PI. LVI. fig. 7). The terminal rays of the oxyhexaster are usually 

 straight (PI. III. fig. 1 ; PL XVII. fig. 8), but slight curvature frequently occurs. In 

 such cases the rays are either simply convex internally or externally (PI, XXI. fig. 6 ; 

 PI. XIII. fig. 6), or they are S-shaped (PI. LXII. fig. 5). The terminal rays may be 

 sometimes quite irregular and wavy, or else hook-like (PI. XIV. fig. 13; PI. XV. fig. 9), 

 or even sharply bent (PI. XXVI. fig. 7). 



Striking forms which occur in many Euplectellidse and here and there in Cratero- 

 morpha, may be termed brush-rosettes, " graphiohexasters." The principal rays are much 

 broadened and bear a bundle of long, straight, thin, terminal rays in parallel or slightly 

 diverging disposition (PL XV. fig. 19; PL XII. fig. 5). A closely related form, 

 distinguished, however, by the slightly waved curvature of the delicate terminals, is 

 represented in PL CIV. fig. 4. In many rosettes with numerous S-like terminal rays, 

 disposed in concentric circles, there is a certain resemblance between the tuft of rays, 

 and a down-feather or pluma. I have, therefore, called these forms " plumicomes." 

 Their individual terminal rays may run to a point at the outer extremity, or becoming 

 gradually thickened towards the curved ends, be rounded ofi" terminally (PL LIV. 

 figs. 4, 6). 



A perfectly uniform increase in the thickness of the straight terminal rays, on to the 

 broad, rounded, free extremity, is exhibited by an unusually large form of rosette, which 

 is also further characterised by a fringe of strongly bent booklets (PL LX. fig. 3). 

 Another form, represented in fig. 2 on PL LXX. , is characterised by the sharply truncated 

 cylindrical thickening of the outer part of the straight terminal rays, which thus exhibit 

 a certain resemblance to the spikes of a Typha. 



In the rosettes with rounded terminal knobs, " sphasrohexasters," the terminal rays 

 occur in varied form. They may be quite straight (PL CI. fig. 7), simply curved, S-shapcd 

 (PL XCT. fig. 7), or finally irregularly curved in a wave-like fashion (Pi. LXXVIII. 

 fig. 12). They are of equal thickness throughout their whole length. 



Where transverse terminal discs are developed in the discohexasters, the stalks 

 seldom retain a cylindrical form (PL XII. fig. 4), but are as a rule thickened either 

 externally or internally (PL XII. fig. 8 ; PL XIII. fig. 3). The terminal discs are fixed 

 transversely on the corresponding terminal ray by their centre, or they may form an over- 



