I2 S PORIFERA. II. 



sclera: the skeletal spunks oxca o-68 — o-g8""", the dermal spicules tornota approaching oxea 0-45 — o-<5 ■,-""",• 

 microsclera of one form, isochela arcuatm 0-034 — 0-0429""". 



This species is most frequently markedly club-shaped. The specimens in hand that are not 

 torn off from the under-layer are attached to larger or smaller stones. At the place of attachment 

 they have a quite slight basal expansion, from which they rise increasing more or less evenly in 

 thickness; thus no real stalk is formed, but the thinnest part is always found just above the basal 

 expansion. Sometimes the upper part is more or less regularly cylindric like the lower part, but most 

 frequently it is more or less compressed, sometimes in such a way that one side is convex, the other 

 flat or concave. Most frequently the club-shape is rather slender, but it may be shorter and thicker. 

 In a few cases the form is a little modified, the upper part being a little lobate; thus we have one 

 specimen, which is, almost through its whole length, divided into three wing-like lobes. In one case 

 the club is divided above into four quite short processes provided with oscula. The largest specimen 

 is ca. cp™" 1 high; it is compressed, and has a breadth of ca. 50""", and a thickness of ca. i2 m,n , just 

 above the basal expansion the thickness is ca. io mra . The smallest specimen, which is more cylin- 

 drical, is 24 mm high and 7 m,n thick. The consistency is rather firm and, on account of the skeleton, 

 rather solid, and it is also somewhat elastic. The degree of contraction of the sponge causes, however, 

 a considerable difference with regard to the consistency, the most contracted ones being considerably 

 harder than those not contracted. The colour (in spirit) is in most specimens light gray (stations 20 

 and 36); in some specimens it is a little darker with a brownish tint, so that it becomes light grayish 

 brown (station 18). The surface is very characteristic, but it has a rather different appearance, accord- 

 ing as the sponge is contracted or not Its appearance is most characteristic in the highly contracted 

 individuals; in these it is closely set with rather deep grooves separated by narrow, ridge-shaped walls; 

 these walls form a peculiar net all over the sponge, imparting to it an appearance highly recalling 

 that of Nardoa reticulum. The less contracted the sponge is, the flatter these grooves become, and 

 they may also quite disappear. The grooves are nothing else than those occurring in so many sponges, 

 for instance in AL incrustans, which are formed by the dermal membrane being sunk between the 

 parts of tissue separating the subdermal cavities, but they are here more regular and always sharply 

 bounded from each other. The less contracted the sponge is, the larger and more shallow are the 

 grooves, while they become smaller and deeper in the contracted sponge, and in this latter they are 

 often oval. Their size is between about 0-4 and 3 mm . The grooves, especially in the contracted sponge, 

 have a rather sharp edge. The surface is so far shaggy, as the dermal spicules project a little every- 

 where between the grooves. The dermal membrane is an exceedingly thin, transparent film, resting 

 on the bundles of dermal spicules projecting from the ridge-shaped walls, and stretched over the inter- 

 jacent subdermal cavities. The pores are situated in the parts of the membrane stretched over the 

 subdermal cavities, and these parts are accordingly pore areas; in these areas they are found in large 

 numbers and very close-set, so that the membrane becomes a sieve. Their size was measured to 0-03 

 — o-4o mm . Oscula are found to a number of from one to ca. ten, evidently in proportion to the size of 

 the sponge. They are found on the top of the sponge or a little down on the side; the largest speci- 

 men shows ten oscula, but it is somewhat damaged, and has perhaps had more than ten; they are all 



