Mr. H. J. Carter on two HexactinelUd Sponges. 123 



the growing margin of the orifices at the circumference to a 

 lamina l-24th inch thick in the fixed or oklest portions at the 

 hase. Spicules of three kinds, viz. skeleton-, subskeleton-, 

 and flesh-spicules. Skeleton-spicule sexradiate ; arms spined 

 throughout, pointed in the smallest, infiated at the extremities 

 in the largest specimens, 5- to 40-6000ths inch long with 

 proportionate thickness (fig. 4). Subskeleton-spicules of two 

 forms, viz.: — 1, acerate, straight, fusiform, attenuately pointed, 

 spined throughout, spines all inclined one way and more or 

 less closely applied to the shaft, 200- by 2-6000ths inch in 

 its greatest diameters (fig. 5) : 2, scopuline spicule, consisting 

 of a shaft and head (fig. 6 and fig. 3, e) ; shaft cylindrical, 

 abruptly pointed at the free end, quadrangularly inflated at 

 the other, microspined throughout, most evidently towards the 

 free end, 68- by l-6000th inch in its greatest diameters 

 (fig. 6, a) ; head consisting of four arms respectively supported 

 by the four angular projections at the end of the shaft, at first 

 running parallel or slightly curved towards each other and then 

 expanded ; arm much thinner than the shaft, inflated globu- 

 larly at the extremity, microspined throughout, especially 

 towards the inflation, where the spines are long and inclined 

 backwards, leaving the convexity of the inflation smooth or 

 bald, ll-6000ths inch long (fig. 6, b, c). Flesh-spicule a 

 hexactinellid rosette, each arm bearing four capitate rays 

 expanded enJleMr-de-Us^ 7-6000ths inch in diameter (fig. 7 

 and fig. 3, /"), or without extended arms, the latter being 

 reduced to a central point, from which the rays radiate in all 

 directions so as to present a globular form, 15-6000ths inch 

 in diameter (fig. 3, <;). Skeleton-spicules free and minute at 

 the growing margin, afterwards becoming larger and enveloped 

 in the vitreous fibre, or distributed throughout the whole 

 structure, from the youngest to the oldest developed part, in a 

 minute form, where one arm is frequently attached vertically 

 to the smooth fibre (fig. 3, dd). Acerate subskeleton-spi- 

 cule sparsely distributed. Scopuline spicule very numerous. 

 Flesh-spicules also numerous. Vitreous fibre smooth between 

 the knots (fig. 3, a a a), which are globular and spino-tuber- 

 culated all over, except where interrupted by their union with 

 the fibre (fig. 3, bb b), or by the projection of one or more 

 arms of the sexradiate spicule in the form of large spines, 

 thickened or elongated, pointed or inflated at the extremity, 

 and spinulated throughout (fig. 3, c c c) j thickest smooth 

 fibre 15- to 19-6000ths inch in diameter. Size of specimen 

 3x4x2 inches. 3 inches high. Last-formed tubo-branch 

 (viz. at the summit) 4-12ths inch in diameter : first-formed 

 branch (viz. at the base) 2-12ths inch in diameter. 



9* 



