276 Mr. H. J. Carter on a new 



the tortuous tubular cavities coming close to the surface on 

 each side. Microscopic structure of the surface also composed 

 of the same form of nail-like spicules, but exceedingly minute, 

 and with their arms all spiniferous, not smooth, and their 

 shafts directed outwards instead of inwards ; their crucial 

 heads applied to the arms of the larger body-spicules, or so 

 inserted into the dermal sarcode filling up the interspaces of 

 the latter as to form, by the intercrossing of their arms, a 

 minute rectangular network or veil, in the interstices of which 

 respectively the pores are situated, — the shafts of these spicules, 

 which are just visible to the naked eye, being so thickly 

 spined, so numerous, and so close together all over the sponge, 

 both inside and out, as to present a continuous white layer, 

 interrupted only by the heads of the largest nail-like spicules 

 of the body and the projecting tufts of long linear spicules 

 towards its lower part. Spicules of five kinds, viz. : — 1. The 

 nail-like spicule of the body, which is smooth in all its parts, 

 and glistening throughout, consisting of a shaft of variable 

 length and head of four arms, also variable in length in the 

 same spicule and generally ; arms slightly curved towards the 

 shaft and parting at right angles from the end of the latter, 

 leaving a rectangular smooth area in the centre, which, from 

 its glassy transparency and dark appearance in situ, forms, 

 with a portion of the arms which is also uncovered by the 

 white dermal crust, a remarkable feature. 2. The linear or 

 fusiform spicule, which may be smooth throughout or partially 

 or entirely spined. It varies in length from microscopic 

 minuteness to two inches long, the latter or long ones alone 

 possessing a double hook at the free extremity. The spines 

 of the minute forms vary in their amount of inclination to 

 the shaft, being in some spicules almost parallel with it, while 

 in others they are widely divergent, and for the most part 

 directed frot7i the sponge, but not always. In the larger and 

 longer forms, of which there are also two kinds, the shaft is 

 either smooth up to its termination in the double hook, or at 

 first smooth, then spiniferous, and just before it terminates in 

 the double hook smooth again, the spines being directed 

 towards the sponge. At the commencement of the spiniferous 

 portion in the latter (for that in the sponge is comparatively 

 smooth) the spines are wide apart and hardly perceptible, but 

 by degrees increase in size, number, and approximation as the 

 shaft of the spicule increases in size, when they may be 

 observed to form a spiral line round it, much like the bracket- 

 steps of a flagstaff, which again passes into single separate 

 spines, as above stated, just before its termination, the shaft 

 also again reappearing for a short distance in a smooth but 



