PORIFERA. III. 



99 



Of this interesting species we have one specimen growing as a small incrustation on an Ony- 

 chocella; its greatest extent is 8 mm , and it scarcely reaches o-5 mm in thickness. The colour (in spirit) 

 is greyish. The surface is hispid on account of the projecting skeletal styli. The dermal membrane 

 is a thin film, it shows a multitude of larger and smaller circular openings representing I think both 

 oscida and pores. 



The skeleton. The dermal skeleton consists of single dermal spicules or of small bundles of 

 these, stretching from the main skeleton to the surface in a more or less oblique direction. In the 

 membrane itself there are no horizontal spicules. The main skeleton has the common construction, 

 consisting of vertical acanthostyli with the heads placed on the substratum; the longest of the styli 

 project beyond the surface, thus causing the hispidity of this; the skeleton is somewhat dense. At the 

 base there is an amount of spongiu, which is only slight but forms however a continuous basal lamella. 



Spicula: a. Megasclera. i. The skeletal spicules are acanthostyli which are more or less, 

 generally only slightly, curved; they are thickest at the base but have no distinct head, and they 

 taper into a long apex. The larger styli are spiued at the base, but the spines are not large and 

 outwards they become smaller and gritty, and they soon disappear; the small styli are generally 

 straight, they are spined in the whole length, and the spines are relatively larger than in the long 

 styli. The styli vary much in size, but there are no separated groups. The length is cri2 — o-65 mm 

 and the thickness at the base o-oi— cro24 rora . 2. The dermal spicules are of a characteristic shape 

 and may best be termed oxytornota; they are rather thick and much thickened about the middle, so 

 that they are strongly fusiform; they taper towards each end, one end is tornote-shaped, or sometimes 

 more rounded, and terminates in a little mucro, the other end is of an oxeote shape, tapering some- 

 what evenly, but the outermost point is generally short; in some cases this latter end is so short 

 pointed and has such a shape that the spicule might be termed a tornote. The spicules are often 

 somewhat curved near the short pointed end. The length is o-22 — o - 268 mm , and the diameter in the 

 middle is o - oo8 — 0'0i7 mm . b. Microsclera are of three forms, chelse of two forms and sigmata; the 

 chelse are ordinary chelse arcuatse and peculiar chelae, i. The ordinary chelse arcuatse have an 

 evenly curved shaft, the alae are somewhat claw-shaped triangular, the tooth elliptical; the length is 

 cro2i — o-o25 mm an d the thickness of the shaft about 0'002 mm . 2. The peculiar chelse are spicules, 

 which are somewhat difficult to understand; they consist of a curved shaft the ends of which are a 

 little dilated and from this dilatation a few processes are produced; the processes may be of different 

 number and differently, often quite irregularly arranged, but generally there are two larger processes 

 at the end of the dilated part, and behind these two others, generally smaller processes; it is probable 

 that the two larger processes answer to a cleft tooth, and the other small processes to alee, but this 

 it is for the present not possible to decide with certainty; on the other hand I consider it as certain, 

 that the spicule is a chela and not a sigma. In spite of the number of processes at each end I think 

 however, that it cannot at all be considered as an ancora; the whole shape of the dilated end-parts 

 seems to me to point towards a chela. The length of this spicule is o-02i— o - 026 mm and the thickness 

 of the shaft is about o-oo28 mm . 3. The sigmata are of a very characteristic shape, they are rather 

 large but exceedingly fine, generally they are strongly curved in the middle and the arms have a 

 hook-formed bend at the end; sometimes they are more evenly curved; they are more or less contorted. 



13* 



