Mr. II. J. Carter on Tetliya casula. lOo 



" Tethya^' for the sponges of whiili I'ttJii/a craniiini is the 

 t}'])*', aiul a(l<)j)t Xardo's name of ^■^ Donntia''' for those of 

 wliich Tetlii/(i /i/nrnrium'iA the type — thus a})i)lying tlie fornu-r 

 to Schmidt's l\ttlla cujilocainits ami T. poli/u)-aj which are 

 genuine species of the group of Tethya craniitm, and to the 

 tour others which I have described and ilhistratcd in the 

 ' Annals ' under the specitic designations of tiactyloidea, ara- 

 bica, atroj}urj)urea, and casula. 



EXPLANATION OF PLATE IV. 



Fit/. 1. Tcthjia casula, n. sp., natuml size: a, head or body; hh, conical 

 I'xnatision, which, in si'fit, is imbedded in the sand; c, fringe or 

 ciliated border; d, sand. 



Fig. 2. The same, portion of surface of body, magnified, to show poly- 

 gonal arrangement of lines of projecting spicules, indicating :— 

 a, pore-areas ; b, vents. 



Fiff, 3. The same, cilium or free extremity of radiating bundle of spicules 

 in conical expansion, magnified, showing : — a a a, bundles of 

 spicules constricted at the margin ; b, continuation of bundle in 

 a cylindrical form ; c, free extremity a little expanded, consisting 

 exclmiveli/ of the forked ends of the long trifid spicule ; d, agglu- 

 tinated grains of sand still adhering to the bundles. 



Fiff. 4. The same, trifid end of forked spicule of cilium, magnified, on the 

 scale of l-12th to l-GOOOth of an inch: a, neck, slightly con- 

 stricted ; b, axial canal. 



Fifl. 5. The same, spicules magnified fourteen times their natural Jenrfth, 

 relatively : a, trifid forked spicule of bundles of conical expan- 

 sion ; 6, straight, long, fusiform, acerate spicule of the same ; 

 c, thick, short, curved spicule of the body-substance ; rf, e,f, real 

 lengths of the same respectively. 



Fifj. G. The same, specimen of each form of spicule, magnified, on the 

 scale of 1- 12th to l-1800tli of an inch, to show their relative 

 thicknesses respectively : a, trifid forked spicule of bundles of 

 conical expansion ; b b, half-length of straight, fusiform, acerate 

 spicule of the same ; c c, half-length of thick, short, curved, 

 acerate spicule of the body ; d, unequal-armed, minute, trifid spi- 

 cule of the sarcodc of the body ; e, minute, bihamate, contort, 

 C- and S-Uke spicules of the same. 



N.B. Part of the half-spicule has been taken out in the figures 

 b b and e c, for convenience. 



Figs. 7 & 8. The same, minute forms of spicule in fig. 6, d^ e, magnified, 

 on the scale of l-12th to 1-fiOOOth of an inch. 



Fig. 9. The same, head of large, trifid, forked spicule of body-substance, 

 magnified, on the same scale, to contrast with the trifid head at 

 the circumference of the conical expansion, fig. 4. 



N.B. In the body, besides the minute spicules with which the 

 Barcode is densely charged (fig. 6, d, e), there are straight acerate 

 and trifid spicules, similar to those of the conical expansion, of 

 various lengths and sizes, together with slight variation in the 

 foiTn of the trifid heads, but all much shorter in the shaft. 



Ann.dc Mag. N. Hi.'if. Ser. 4. Fo?. viii. 



