PORIFERA. II. 217 



This species is inerusting, or, when growing thicker, of a more massive form. In the exterior 

 it is somewhat similar to the preceding species, being set with papilke of a similar structure as in 

 M. elliptica. In the quite inerusting individuals the papilla; seem to be wanting, and in those only little 

 thicker to be present in rather slight number. The species grows on various bottom material, stones, 

 shells, or more loose material. The largest specimen has a greatest extent of fully $o mm , and is pro- 

 vided with many papillae, two smaller, about inerusting, specimens have few papillae, and an inerusting 

 specimen with an extent of 15""" and a thickness of ca. 2'5 mm shows no papillae. Schmidt describes 

 the exterior of the species as «Unregelmassige Knollen und Fladen», and Vosmaer figures a speci- 

 men, which probably belongs to this species and seems to be regularly cushion-shaped, with an extent 

 of fully 50 mn> . Accordingly the species does not seem to equal the preceding one in size. The colour 

 (in spirit) is grayish. The consistency is as in the preceding species or a little looser. The surface is 

 smooth, without projecting spicules. The dermal membrane is also here a solid, easily separable mem- 

 brane with close-lying spicules. Oscula and fores: What was said with regard to oscula and pores in 

 the preceding species, holds also good of the present one; also here pore papillse are found of different 

 sizes and stages of development, and conical, spout-shaped oscula. 



The skeleton. The dermal skeleton, as in the preceding species, consists of spicules lying hori- 

 zontally in the membrane and arranged in more than one layer. In the present species they are 

 generally not so close-lying as in the preceding one, but with regard to this fact some variation may 

 be found in the present species; where they are least close-lying they are scattered without any order, 

 and the membrane may everywhere be seen between them; where they are most close-lying, a tendency 

 to an arrangement in bundles may be observed. The skeletal structure in the pore papillae and the 

 oscular walls is like that in the preceding species. The main skeleton is almost exclusively poly- 

 spicular; some rather powerful fibres are found passing from the base towards the surface and towards 

 the dermal membrane, which they support. The fibres are only mutually connected to a very slight 

 degree, and generally only by single spicules which are irregularly scattered and only found sparingly. 

 The polyspicular fibres may attain a thickness of 0-09 — cri2 ram . In the lower part of the sponge, which 

 is turned towards the underlayer, sand and gravel is generally embodied copiously. Spongin is found 

 in the nodes and in the fibres, it is white and clear and therefore not easily observed; it is not copious 

 although distinctly present, and it seems often to coat the fibres completely, but with a scarcely per- 

 ceptible layer. 



Spicida : a. Megasclera are of one kind only, and consequently of the same form in the dermal 

 membrane and the other parts of the skeleton. They are tylota with slightly swollen ends, sometimes 

 the ends are so slightly swollen, that the spicules approach to or are strougyla. They are straight or 

 slightly, most frequently a little irregularly, curved, and they are slightly fusiform. Their length varies 

 from 0-44— o-6i mm , and the thickness in the middle is croio— o-oi4 mm . A few developmental forms were found; 

 they showed that the spicules are begun as mouactinal; the finest one had one end rounded, the other 

 short pointed; as long as the spicules are not fully developed, they show a rather distinct difference 

 between the two ends, one being thicker, the other a little thinner with a most frequently more marked 

 swelling; still in the fully developed forms this difference may often be seen. 



The Ingolf-Expedition. VI. 2. 28 



