1 86 PORIFERA. II. 



The skeleton. The dermal skeleton, as far as I have been able to judge from the material, consists 

 of bundles of dermal spicules more or less erect, but most frequently so highly recumbent as to be 

 lying almost or quite horizontally in the membrane. In places they may become short fibres. The 

 main skeleton is quite irregular and consists of a diffuse network of loose spicula-buudles and single 

 spicules, but fibres are not formed, at most loose, band-like strings. Spongin is found in the skeleton, 

 chiefly cementing the ends of the spicula-bundles, but it is only present to a very slight amount, and 

 is only to be observed with difficulty. 



Spicula: a. Megasclera. i. The skeletal spicules are styli, more or less curved, only rarely 

 straight, they are evenly and middle long to rather long pointed; generally they are a little tapering 

 towards the rounded end. Their length is rather constant and is between 0-51 and o-6o8 mni , most 

 frequently nearer to the latter size, the thickness is 0-013 — o-oic/" m . Developmental forms, down to 

 quite fine ones, were seen singly. 2. The dermal spicules are tylota, they are almost always 

 straight, at most quite slightly curved, and they are a little thicker in the middle than towards the 

 ends. Their length is somewhat varying, from 0-298 — o-38 mm , and the thickness is 0-005— 0-009™ m . A 

 few developmental forms were seen, of which the finer ones have one end distinctly thinner than the 

 other, b. Microsclcra; these are of two forms, isancorse unguiferse and birotulae. 1. The an corse 

 have an evenly curved shaft and a number of from five to eight teeth at either end. Alse are not 

 found, but besides the mentioned number of teeth that are free, one or two teeth are found running 

 down the dorsal side of the shaft and coalesced with it. The one or two teeth thus connected with 

 the shaft grow considerably longer than the free teeth; their form and the way in which they are 

 connected with the shaft are quite irregular, sometimes one is situated just at the dorsal side, some- 

 times they are found one at either side, or one more at the side, the other more behind. Also the 

 free teeth show some irregularity, some being broader than others, which is dependent on their 

 number. The number of teeth may also be different at either end. The length is 0-054 — o-o657 mm , 

 and the thickness of the shaft is 0-0050 — o-oo57 m '". A few developmental forms were seen, the youngest 

 ones showed only a knob-shaped expansion at either end. 2. Birotulse have a straight shaft, and at 

 either end a circle of nine to fourteen narrow, inwardly curved teeth. As the number of teeth is upon 

 the whole varying, it may also be different at the two ends. Some irregularity may also here be 

 found in the form, as some teeth may be broader than others. The length is 0-015 — o-oi8 mm , sometimes 

 up to o-02i mm , the breadth across the teeth is 0-004 — o-oo6 mm , and the thickness of the shaft ca. o-ooi mm . 

 The microsclera are found throughout the sponge, but are especially seen in the dermal membrane; 

 birotulse are the most numerous ones. 



Locality: Station 89, 64 45' L,at. N., 2j J 20' Long. W., depth 310 fathoms, a small fragment; 

 6i° 09' L,at. N., 7 54' Long. W., depth 180 fathoms, one specimen (Ad. Jensen, the cruise of the « Michael 

 Sars 1902). The two localities are situated in the Denmark Strait and south of the Faroe Islands. 



2. I. oxeata n. sp. 



PL VI, Fig. 6. PI. XVIII, Fig. 2 a— f. 

 Thickly incrnsting, massive or irregularly lump-shaped or roundish. The surface almost smooth. 

 Flit dermal membrane a thin film, supported by penicillatc, erect, or more or less recumbent bundles of 



