355 
to our Knowledge of the Spongida. 
Varieties of both these types are represented, in Dr. Bower- 
bank’s 1 Monograph of the British Spongiadae,’ as u defen¬ 
sive spicula”—the former under the designation of “spinulo- 
multiangulated cylindrical ” (vol. i. p. 239, pi. iii. fig. 72), 
and the latter under that of u vertically-spined cylindrical ” 
(ib., ib. fig. 69). 
Each type, like those already mentioned in my u Notes, 
&c.,” presents itself under a great variety of forms; and 
although it is necessary to remember these forms in connexion 
with the species to which they belong, yet it is equally neces¬ 
sary that the respective typical ones upon which each group 
is constructed should be first understood. 
The Spinispirula. 
Spinispirula, as its etymology indicates, is a spiniferous, 
spirally twisted spicule (ex. gr. PI. XXVI. fig. 14, a, and 
PI. XXIX. fig. 11), which may be long or short, thick or 
thin ; thus in Rhaphidhistia spectabilis (PI. XXVI. fig. 14, a) 
it is long and thin ; while in the Suberite from the crab’s 
back to be hereafter mentioned (PI. XXIX. fig. 12) it is 
short and thick. Again, the spines may be long and thin, 
as in Dactylocalyx Masoni , Bk. (Proc. Zool. Soc. 1869, pi. vi. 
fig. 4); or long and thick, as in D. Bowerbankii , Johnston 
(ib. fig. 8, b), or obtuse (ib. fig. 8, a). The sjiines may be 
arranged on the spicule in a spiral line, corresponding with 
that of the shaft, as in Rhaphidhistia spectabilis and Spongia 
Dysoni , Bk. (/. c.), or they may be scattered over the shaft 
less regularly,—in all cases over the extremities, and some¬ 
times entailing an elongation of the surface of the shaft 
(PI. XXIX. fig. 11). Lastly, the shaft may consist of many 
or be reduced to one spiral bend only, as in Rhaphidhistia 
spectabilis and Hymeraphia spiniglobata (PI. XXIX. figs. 14, a, 
and 16, d) respectively, when the latter may pass into a glo¬ 
bular form, hence Schmidt’s name u Spiralstern ” (Spong. 
Kiiste Algier, p. 17). 
To convey an idea of the plan upon which the Spinispirula 
and its varieties are formed, let us conceive a thin globe of india 
rubber over which a number of spines are arranged in a spiral 
or less regular manner, the spiral line having its poles opposite 
each other; now let the globe be more or less elongated in 
the direction of its axis, and at the same time twisted, when 
it will be possible to represent thereby most of the varieties 
of the Spinispirula. In many instances, the transparency of 
the spicule allowing all its spines to be more or less seen at 
once, it will be necessary to study their arrangement carefully 
by altering the focus of the magnifying-power, when the 
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