Hcxactinellidaj and Lithistidae. 467 



fig. 19 (which is identical with the latter) appears to be atransi- 

 tionary form to fig. 20, which is the long-spined spicule peculiar 

 to A. beatrix. 



N.B. The dotted lines indicate that the spines themselves 

 are microspined. Figs. 18-20 are all on the scale of l-12th to 

 l-6000th of an inch. 



Flesh-spicules of Hyalonema, &c. 



Birotulate, consisting of a sparsely spined straight shaft, termi- 

 nated at each end by eight separate blades, which are recurved, 

 dome-shaped towards the centre. Hyalonema Sieboldii, Gray, 

 &c. 



Birotulate in a sexradiate form, showing its analogy to the 

 "rosette." Hyalonema Sieboldii. Sparse. 



N.B. The birotulate may have two, four, or six heads, accord- 

 ing with the development of the elementary cell of the spicule 

 into two, four, or six arms — that is, a simple shaft, a cross, or 

 sexradiate. 



In like manner, the rotulate heads may be absent, and the 

 shafts thickened and covered with short, conical, vertical spines 

 either at the extremities only or throughout (see Bowerbank's 

 Brit. Spong. vol. i. pi. vi. fia - s. 153-157). 

 Fig. 23. Rosette with straight pointed rays, in which the arms have 

 become enveloped by vitrified sarcode so as to form a spherical 

 centre. Euplectella cucumer. 

 Fig. 24. Rosette with straight capitate rays, in which the same thing has 

 taken place, but the vitrified mass has gone beyond the arms of 

 the rosette : a, main fibre ; b, portion uniting rosette to main 

 fibre. Dactylocalyx pumiceus. 



N.B. The last two forms point out the transition of the 

 rosette to the siliceous globules and stellates (which are also 

 " flesh-spicules ") in the Geodinida?, &c. ; while the junction of 

 this rosette with the main fibre is the only instance in which 

 I have met with a flesh-spicule involved in the skeleton- 

 structure. 



Plate XIV. 



Anchoring-spicides. 



Fig. 1. Spiniferous anchoring-spicule of Lubaria JiemispJicerica, Gray, 

 showing form of head or free end : a, head ; b, undulating line 

 on head, which has its projecting curves prolonged into spines 

 in Euplectella (see figs. 4 & 5) ; c, portion of shaft, whose upper 

 or fixed end is smooth and attenuated ; d, spines on shaft ; 

 e, position of cross on central canal. 



Fig. 2. Smooth anchoring-spicule of Labaria hemisphcericu, showing 

 form of head or free end : a, position of cross ; b, usual inflation 

 of shaft just before expansion into head (here there is no undu- 

 lating line on the head, which is more or less compressed) ; 

 c, portion of the smooth shaft. 



N.B. These two forms in Labaria are relatively magnified and 

 taken from the larger specimens of their kind. The upper or 

 fixed end of the shaft is not figured, neither is the intervening 

 portion between it and tha't given ; but the former is the same 

 in all the anchoring-spicules, viz. smooth, attenuated, and firmly 

 fixed in the sarcode of the body ; while the latter or intervening 



