PORIFERA. II. 



163 



or lobes may rise; but most frequently it seems, when rising, to assume a somewhat compressed form, 

 always, however, forming some stubby lobes. Thus the roundlobed form is the most marked character 

 of its exterior. The specimens in hand, none of which are quite entire, reach a rather considerable size; 

 a specimen of a massive and more expanded form has a greatest extent of ca. ioo ram , and a greatest 

 height of ca. go™ 1 ", the thickness of the expanded part is ca. 30""". The largest of the more erect and 

 compressed specimens has a breadth of i25 mm , a thickness of ca. 40 mm , and a height of ca. 8o mm . Thus 

 these specimens are considerably larger than that of Fristedt, which had a length of 40 mm , a breadth 

 of i5 mm , and a thickness of 20 mm ; according to these measures his specimen must have been of massive 

 form. The colour (in spirit) is whitish yellow. The consistency is rather brittle and only little elastic. 

 The surface is very slightly grooved; only here and there the grooves were a little deeper, in other 

 places the surface is quite smooth. We have here in reality the same structure as in several Myxilla- 

 and Lissodendoryx-species with grooves separated by ridges, only that here the grooves are very shal- 

 low or disappearing and the ridges little conspicuous 1 ). The surface gets, however, a somewhat net- 

 like appearance, the subdermal cavities situated under the grooves shining through with a darker 

 colour. The surface is in most places very finely shaggy from projecting spicules. The dermal mem- 

 brane is a somewhat transparent, not especially thin film. It is supported by bundles of dermal spicules, 

 which may be highly recumbent. In most places, especially where pores are found, the membrane 

 gets a peculiar appearance, about as mentioned under M. incrustans. The subdermal cavities, which 

 shine darkly through the membrane, are here distinctly seen; sometimes they are somewhat roundish, 

 sometimes more irregularly sinuous, and separated by the parts of tissue between the canals, which 

 appear whitish. The darker areas over the subdermal cavities, however, are subdivided into smaller 

 areas, fibres or parts of tissue stretching from the edges of the subdermal cavities below the suspended 

 membrane. The pores are then situated in the areas that arise in this way. Therefore the sponge, 

 as to its surface, is very similar to such specimens of M. incrustans as have a tolerably smooth sur- 

 face. The pores are lying in groups in the mentioned areas of the dermal membrane, and thereby these 

 areas become pore-sieves. The pores are round, or, when placed close together, irregularly polygonal; 

 their size was measured to 0-03 — o - 23 ram , sometimes they were still larger. Oscula are scattered and 

 only few in number; they are round or sometimes more irregular openings, surrounded by the dermal 

 membrane with a sharp edge. They are very varying in size and reach at most a diameter of ca. 4 mra . 

 The skeleton. The dermal skeleton consists of penicillate bundles of dermal spicules, which 

 pass out from the skeleton below and support the dermal membrane, piercing it. Where the membrane 

 is lying over the parts of tissue separating the subdermal cavities, the question is only of bundles, 

 which are perpendicular or more or less recumbent. From the edges of the subdermal cavities shorter, 

 a little branched fibres run into the suspended membrane, where they end, spread in a penicillate way, 

 and finally fibres run under the suspended membrane, or more loosely lying dermal spicules are found 

 in the strings of tissue that pass under it, and in both cases more or less erect, penicillate bundles 

 project from here through the membrane. Moreover, the membrane is highly filled with microscleres. 



') I suppose the structure of the surface in these species to be owing to the strength of the dermal membrane; thus 

 M. incruslajis has a thin dermal membrane and deeper grooves, M. fimbriata a thick dermal membrane and a smooth sur- 

 face, and in both respects the present species occupies a position about midway between these two species. 



21* 



