390 , Mr. H. J. Carter on 



narrow, club-like inflation of the shaft; (fig. 7,b) the infla- 

 tion becomes enlarged towards the upper part, a tubercle is 

 developed at the summit, and an indistinct row of small 

 spines around the widest portion ; (fig. 7, c) the tubercle 

 passes into the form of an umbo, the row of spines into a pro- 

 jecting coronal structure, cut off by hour-glass contraction 

 from the lower part of the inflation, over which are developed 

 several other small spines which assume a more or less sub- 

 sidiary coronal arrangement at the upper part ; (fig. 7, d) the 

 umbo disappears, and the summit becomes simply convex or 

 dome-shaped, while the spines of the coronal structure still 

 more project, are increased in size and reduced in number, 

 the spines of the constriction below have also disappeared, and 

 the upper part of the once simply inflated head is now found 

 to be capped by the new development or corona ; (fig. 7, e) 

 finally the coronal spines may be greatly increased in size 

 and reduced even to four only, the original ovular inflation still 

 more constricted in the centre and its upper part devoted to 

 the support of the four spines. Of course there is every inter- 

 mediate form to be seen, from the simple, elongated, ovular 

 inflation to the head with four simple spines, but "c" and 

 "t?" appear to be the most common. For this spicule, 

 which also requires a lengthy description and is probably 

 common to the Farreas, I would propose the name of " cla- 

 vula." As with the dermal sexradiate, so witli the clavula 

 here, and indeed the barbula also, the development of the 

 7nacrospmed appears to be but a sequence of the ?mc?"ospined 

 or simply smooth form. (But this is only what occurs gene- 

 rally throughout the development of a sponge-spicule, as I 

 have long since stated, viz. " first the simple form and then 

 the ornamentation.") (4) The rosette; sexradiate, consist- 

 ing of four straight arms without central inflation, terminated 

 respectively by four divergent rays around a central one ; 

 rays smooth and simply pointed, or more or less capitate and 

 microspined, varying in number in each instance ; average 

 diameter of entire spicule, i. e. the rosette itself, about 15- 

 GOOOths in. (fig. 6 and fig. 9, a b). (5) A smaller sexradiate 

 with all four arms equally developed ; arms straight, pointed 

 and spiniferous, issuing from the centre, which at first is not 

 inflated, at equal angles to each other; variable in size, 

 under 8-1800ths in. in diameter, and a variety of the fore- 

 going (fig. 2, a b, and fig. 10). The dermal sexradiate no. 1 

 is chiefly confined to the surface, where, through the over- 

 lapping of its horizontal arms, it forms a quadrilateral lattice- 

 work whose interstices are tympanized by the dermal sarcode 

 in which the pores are situated (fig. 11). No. 2, the barbula 

 (fig. 3), frequently projects more or less through the lattice- 



