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THE VOYAGE OE H.M.S. CHALLENGER. 
The modifications in the form of the rhabdus most useful for classificatory purposes 
are those which afiect its termination. We therefore distinguish the different forms of 
this spicule by the character of its ends, as follows : — 
(a) Forms of rhabdus with similar terminations. — 
1, Oxea (6^u 9, eta, sharp, pointed) (Fig. X,, a). When the rhabdus is sharply 
pointed at each end it is ^ rhabdus amphioxea ; ^ in nearly all cases in which a spicule 
is similarly terminated at both ends we shall dispense with the prefix “ amphi- ” leaving 
it to be understood, and since the rhabdus oxea is one of the most commonly occurring 
Pig. X. — Modifications of the Ehabdus. a, Oxea ; 6, tornote ; c, strongyle ; d, tylote ; e, oxjdylote; /,tylotoxea ; g, style ; 
h, tylostyle ; j, sphere ; k, plagiotrisene ; I, orthotriaene ; m, protriaene ; n, anatri»ne ; o, aniiihitriaene ; p, crepidial 
rhabdus or rhabdocrepis of a Lithistid desma ; q, the same, more advanced in growth ; r, ditto ; s, ditto, more enlarged ; 
t, the fully developed desma. The dotted line marked o on the left of the diagram passes through the origin of the 
spicules ; the arrows directed from it indicate the direction of growth of the actines, ec, ecactine, es, esactine ; in fig. k 
the cladome is indicated b}' the letters k\ ; in figs, s and t the crepis by Kp, and in fig. t, z indicates a syzygial tubercle. 
spicules we shall omit the substantive “rhabdus” and use the adjective “oxea” in a 
substantive sense. When the actines of other spicules than rhabduses are sharply pointed 
we shall express the fact by the adjective “ oxeate.” The term in Bowerbank’s nomen- 
clature corresponding to oxea is “ acerate.” 
2. Tornote {ropvo^, 6 , a pair of compasses or turner’s chisel. The adjective “tornotus” 
is derived from this) (Fig, X., b). When the rhabdus is very abruptly pointed at 
^ The feminine termination is used in agreement with rhabdus. 
