PORIFERA. II. !8i 



or less free branches that may here and there be attached to the branches of the Hydroid, but may 

 also be quite free; thus, as to its mode of growth, it reminds of Esperiopsis Normanni, and the branched 

 form is the one that is typical and most characteristic of the species. The branches may be variously 

 formed , thicker and more irregular and flattened , or thinner and cylindric. They may branch in 

 different ways, and they may be more or less coalesced, sometimes in such a way as to form plate- 

 shaped parts. When the species is growing on a different substratum, it may form a common incrus- 

 tation, but this seems to be a rare case; we have only one specimen of this form, growing on a large 

 shell of Modiola modiolus. The largest specimens in hand, which may be described as irregular, longish 

 cushions, have a greatest extent of 75"' m . The most frequent length of the more or less branched 

 specimens is ca. 25 — 55""". The consistency is of middle firmness and somewhat elastic, the free 

 branches are soft and flexible. The colour (in spirit) is a lighter or darker brown to grayish black or 

 almost quite black; in some of the jars the sponge has kept its original grayish yellow colour, or has 

 only turned a little darker. The surface, when undamaged, is smooth or at most very slightly shaggy- 

 The dermal membrane is a thin and transparent film, but it is distinct and separable; it has a special 

 skeleton of horizontal dermal spicules, and it is supported by more or less perpendicular pillars of 

 dermal spicules; these spicules may be a trifle projecting. The pores are round; in most places 

 they are lying close together in the meshes of the dermal reticulation , several pores in each 

 mesh. They are rather small, their size being measured to between 0-023 — 0'o83'" m . Oscula are 

 little conspicuous, but they may almost always be found by a closer examination. Most frequently 

 they are more or less hidden at the base of the branches or in the clefts between these, or at other 

 places in folds of the surface. They form most frequently irregular openings, the thin membrane 

 round them being split into lobes; in these lobes the dermal spicules are closely gathered parallel to 

 the longitudinal axis of the lobe, that is to say, with the ends towards the opening. Most frequently 

 the oscular aperture leads into a larger or smaller cavity just under the membrane. Oscula are present 

 in only rather small numbers. 



The skeleton. The dermal skeleton is of a similar structure as in I. piceus, and forms a beauti- 

 ful, in most places rather close, reticulation of polyspicular fibres. The meshes are triangular, quadran- 

 gular, or polygonal. The fibres have rather many spicules alongside, but in this respect they are 

 varying, and accordingly of varying thickness; generally thicker fibres are found having a sinuous 

 course, chiefly in the longitudinal direction of the sponge; between these fibres then thinner ones are 

 found, and sometimes only a few spicules are seen together, or the meshes are divided by single ' 

 spicules. As in the preceding species the fibres are almost always of some length so as to contribute 

 to the formation of several meshes, more rarely they are so short that they only reach from one fibre to 

 the next; the thickest fibres are generally the longest. This structure gives to the dermal reticulation 

 a peculiar, characteristic appearance; the appearance may otherwise be somewhat varying, especially 

 with regard to the closeness of the net of meshes and the thickness of the fibres. The dermal mem- 

 brane is supported by perpendicular or more or less recumbent pillars of dermal spicules, spread in a 

 penicillate way; these spicules may project quite slightly through the membrane, so that the surface 

 becomes very slightly shaggy. The pillars are generally only of the length of one spicule. The main 

 skeleton is a close, quite irregular reticulation, in which there is no distinction between primary and 



