g 2 PORIFERA. III. 



longitudinal direction of the worm-tube, is about 30"""; the incrustation is very thin and reaches where 

 it is thickest scarcely 0-5 mm . The colour (in spirit) is light greyish brown. The surface is somewhat 

 strongly hispid from projecting skeletal spicules. The dermal membrane is a thin, transparent film. 

 Pores and oscula : some circular openings are found in the membrane, scattered on the surface, they 

 were measured to a diameter of o - 023— 0*15 mm ; probably the smaller openings are incurrent and the 

 larger excurrent, but no separation into two divided sizes could be observed. When the sponge is 

 examined with a lens a multitude of canals and cavities are seen in the tissue; they are especially 

 visible, when the sponge is somewhat dry. 



The skeleton. The dermal skeleton; in the dermal membrane the chelae occur numerously, in 

 some places lying rather densely, in others more scattered. The skeleton formed of the dermal spicules 

 is somewhat strongly developed; it consists of bundles or fibres stretching from the main skeleton, 

 often quite from the base upwards and supporting the dermal membrane; the spicules in the 

 bundles are outermost spread penicillately, and they may project a little through the membrane. The 

 fibres have often a very oblique or decumbent direction, thereby being longer, and thus, when the 

 membrane is viewed from above, one may get the impression, that the dermal membrane has a reti- 

 culation. All the dermal spicules have the pointed end turned outwards. The main skeleton is formed 

 of acanthostyli with their head-ends based on the substratum, the longest of them project considerably 

 beyond the surface. There is an amount of spongin at the base, in which the head-ends of the stvli 

 are imbedded, but it is, however, only slightly pronounced. 



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

 generally somewhat curved; the basal end is the thickest part of the spicule, but there is 110 head 

 developed; they taper evenly into a long apex. The small styli are spined in the whole length, and 

 the spines are more or less reclined. In the large styli the spines are relatively smaller, they are 

 present only on the lower part of the spicule and upwards they become small and gritty. The spines 

 on the lowermost part are both in the small and the large styli not specially larger than those a 

 little more upwards. The size of the styli varies greatly, and they are divided into two groups, which 

 show however no other principal differences than the size. The length of the large styli is 0-43 — 

 0-62 mm and of the small 0-14— o - i8 mm , the diameter at the base is 0-017 and oon ram respectively. 2. The 

 dermal spicules are of a characteristic shape; they are styli and have a shape like those in irregularis 

 with the rounded end narrowed and handle-like, but they are not polytylote; they are straight or 

 slightly curved and they have an even, middle-long apex. The length is 0-28— 0-33 mm and the diameter 

 in the middle o - oo8— o , oi2 mm . b. Alicrosclera ; these are chelae arcuats; they have an evenly, rather 

 strongly curved shaft, the end-parts are relatively small, the tooth is lanceolate with a long tuberculum; 

 the alae are of the same length as the tooth, strongly incised in the lower edge and somewhat tooth- 

 shaped; the shaft is not flattened. The length is 0-023— 0-035 mm , an d the diameter of the shaft about 

 0-0038 — 0-005""". The chelae occur, as mentioned, in the dermal membrane, but they are also otherwise 

 seen in the body of the sponge. 



This species is nearly related to the preceding one, II. irregularis, it is however distinguished 

 from this by characteristic differences; thus in contrast to irregularis it is hispid from projecting 

 skeletal spicules, and the chelae do not form a dense laver in the dermal membrane. But the most 



