PORIFERA. II. 



J 95 



thirteen teeth, comparatively long and directed much downward, so as to form a small angle with 

 the shaft. Their lenght is 0-037— 0-05 i mm , the thickness of the shaft is ca. 0-002—0-0028""", and the 

 breadth across the circle of teeth is about o-oio — 0-0128""". A few smaller specimens are seen, down to 

 a length of 0-030""". Not rarely the shaft is slightly rugged or spined, a feature that recalls the similar 

 one in the amphidisci of the Hexactinellida. 2. The small birotulse have at either end eleven to 

 fifteen teeth. Their length is o"Oi8— o-025 min , the thickness of the shaft is ca. d-doii" 1 " 1 , and the breadth 

 across the circle of teeth ca. 0-0057'"'". The small birotulse differ from those of polydentata not onlv 

 by the size, but also by the fact that the thickening of the end of the shaft from which the teeth 

 issue, is flatter and more disc-shaped in affinis than in polydentata. Both forms of microsclera occur 

 throughout the tissue, the small ones being more numerous than the large ones; in the dermal mem- 

 brane the large ones seem especially to occur. 



Locality: Cape Tobin on the eastern coast of Greenland, 70° 23' Lat. N., 2 2° 00' Long. W., depth 

 57 fathoms, one specimen. (The Amdrup-Expedition 1900). 



9. I. spinosa 11. sp. 

 PL VI, Fig. 8. PI. XIX, Fig. 1 a-e. 



Erect, irregularly cylindric? The surface smooth or very slightly shaggy. The dermal membrane 

 a thin Jit in, supported by erect or recumbent bundles of dermal spicules. The skeleton an irregular, 

 polyspicitlar reticulation. Spicula : Megasclera: the skeletal spicules acanthostyli with scattered spinu- 

 latiou 0-40 — o-j2""" . the dermal spicules tylota 0-24 — o-J4""" ; microsclera fivo forms of birotulcs, large 

 ones with eight to twelve teeth o'Oji — o-ojf"", small ones with nine to thirteen teeth 0-018 — 0-024""". 



Of this species, which is especially interesting on account of its spicules, we have only a frag- 

 ment, no doubt the upper part of the sponge. Below, from the place where it has been broken off, 

 and some way up, the sponge is a little compressed, but then it becomes about cylindric with a 

 rounded upper end. According to this, the form might be supposed to have been erect and more or less 

 irregularly cylindric. The height of the specimen is 27""", and the thickness above is 8 mm . The colour 

 (in spirit) is yellowish gray. The consistency is rather brittle. The surface^ in undamaged places, is 

 smooth or very sligthly shaggy. The dermal membrane is a thin film, supported by dermal spicules. 

 Pores are seen here and there on the surface in groups, they are rather large, up to 0-4""". Oscula 

 were not seen. 



The skeleton. The dermal skeleton consists of erect or more or less recumbent bundles of 

 dermal spicules. The main skeleton is a quite irregular, polyspicular network; tolerably distinct fibres 

 are formed, but they have an irregular course, some of them, however, seem to be running towards 

 the surface. A distinct and fairly copious mass of spougiu is found in the skeleton, in many places 

 coating the fibres entirely with a thin layer. 



Spicula. a. Megasclera. 1. The skeletal spicules are acanthostyli with a rather scattered 

 spinulation; they are straight or, most frequently, slightly, not rarely irregularly curved. The point is 

 a little varying, between rather short and middle long. Their length is 0-40— o-52 mm and the thickness 

 ca. o-on— o-oi4 mm . A few developmental forms were seen, the finest ones are about smooth. 2. The 



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