PORIFERA. III. 



8? 



groups; the dermal spicules strongyla with a slight, double curvature. 0-27— 0-45'""'; microsclera cliche 

 arcuatce 0-030 — 0-033""". 



This species forms thinner or a little thicker incrustations on stones; the surface bears a 

 number (in the specimens to hand some few to about a dozen) of long papilla;, which generally reach 

 a length of 6 mm or a little more; they are cylindrical, generally a little thickened towards the apex, 

 and they may vary in thickness from quite thin and thread-like to a diameter of about 0-5 mm . The 

 largest of our specimens has a greatest extent of 25 mm ; the specimen figured by Schmidt I. c. is 35™™ 

 long. The colour (in spirit) is greyish or dirty yellowish. The surface is smooth without projecting 

 spicules. The dermal membrane is a tough and solid, easily separable membrane which is provided 

 with horizontal spicules. Oscula and pores: the mentioned appendages are by Thiele (1. c.) declared 

 to be oscular papillae, and this is also the case with some of them, but the greater part are pore- 

 papillae; the oscular papillae have a simple opening in the summit, while the pore-papillae have here 

 a pore-sieve stretched over the opening. So far as I could see on my somewhat damaged material 

 there is also some difference in the shape of the papillae, the oscular papillae being more conical and 

 the pore-papillae cylindrical and somewhat widened towards the apex. 



The skeleton. The dermal skeleton; the skeleton formed by the dermal spicules is by far the 

 largest part of the whole skeleton. The spicules form fibres which run in different directions quite 

 from the base up to the dermal membrane; these fibres consist of many spicules and are generally 

 rather thick, they may f. inst. reach to a diameter of 0-36 mm . In the skin the spicules lie horizontally 

 and in more than one layer, thus forming a close skeleton; they lie in all directions, but however 

 somewhat bundle-like; the bundles in the different layers generally cross each other. Finally the 

 dermal spicules form the skeleton in the wall of the papillae; they lie here in the longitudinal direction, 

 but the spicules in the different layers crossing each other under acute angles and rather regularly. 

 The main skeleton is formed mainly in the ordinary way of acanthostyli with their heads on the sub- 

 stratum ; they do not reach to the dermal membrane. Where the fibres of dermal spicules rise from 

 the base, they are seen to have just their basal end formed by acanthostyli. Spongin is found at 

 the base. 



Spicula: a. Megasclera. 1. The skeletal spicules are acanthostyli; they are straight or very 

 slightly curved; the basal end is not or only slightly thickened; they taper evenly into the apex, but 

 the outermost point is not long. They are spined in the whole length, on the base the spines are 

 large and radiating, giving thus to some degree the impression of a head-swelling; the spines on the 

 shaft are reclined. The styles vary much in length, but there are no groups. The length is 0-13 — 

 0-27 mm and the diameter at the base 0-017— 0-028 mm . 2. The dermal spicules are strongyla; they are 

 slightly fusiform and have nearly always a curious and characteristic double curvature, more rarely 

 they are somewhat irregularly curved or nearly straight; the length is 0-27 — 0-45 mm , varying a little 

 in different individuals, and the diameter in the middle is 0-007— o-oi2 mra . b. Microsclera are chelae 

 arcuatae; they have a regularly curved shaft, the end-parts are not large, the tooth is elliptical, the 

 alae have generally the lower edge but slightly incised and are more or less triangularly lobe-shaped 

 in side view. The length is 0-030— 0-035™™ an< ^ t ne thickness of the shaft about 0003 mm . The chelae 

 are found rather richly in the tissue quite down to the base, they are often abundantlv present along 



