PORIFERA. III. 



from the main skeleton, often almost from the base, upwards to the dermal membrane which rests on 

 them; above they are more or less penicillately spread; they are somewhat perpendicular or more 

 oblique and often somewhat decumbent. The skeleton in the wall of the oscular and pore-papillse is 

 formed by fibres stretching up in the wall and here forming a skeleton of close-lying, parallel spicules. 

 There is no skeleton of horizontal spicules in the membrane, but this is provided with dense-lying 

 chelae. The main skeleton is of the typical construction formed by vertical acanthostyli with their 

 heads placed on the substratum; the longest of the styli may reach to or near to the surface. Spongin 

 is present at the base, but only to a very slight degree. 



Spicula: a. Megasclera. i. The skeletal spicules are acanthostyli which are divided into two 

 rather well defined groups of sizes. The large styli are straight or generally slightly curved near the 

 head, this latter is small or not at all pronounced; the spines are only present on the head and a 

 little way out, being here smaller and soon quite disappearing. The small styli are straight, the head 

 is very small and for the greatest part due to the somewhat longish, radiating spines; the style is 

 spined nearly in the whole length, only a small apical part being smooth; the spines are often 

 reclined; they are of moderate size or small, and in this respect there may be some difference in 

 different specimens. The length oFthe large styli is 0-41 o-65 mm with a diameter of the head of 

 0-020 0-028 mm , and of the small styli 0-16 O'i9 mm and the thickness of the head about 0-021 mni . 2. The 

 dermal spicules are oxea with transitions to tornota; they are straight and generally more or less 

 fusiform and somewhat long tapering and in this case they are oxea, the thinner ones are more 

 cylindrical with shorter points and must be termed tornota. The length, which may vary a little in 

 various specimens, is on the whole 0-32 0-47 mm with a diameter in the middle of o - oo6 0-014". The 

 spicules have generally not quite equal ends, but one end is slightly thinner than the other; the 

 thinner the spicule is the more pronounced is this difference, and some few very fine developmental 

 stages were quite monactinal, thus showing that the spicule begins as monactinal. Besides the 

 mentioned dermal spicules there are also in this species, as in the preceding one, some thicker, fusi- 

 form oxea, they have a length of 0-29 0-35 mm with a thickness in the middle of 0-015 0-017 "' n '; they 

 are very scarce, and as the measurements show, they seem to be connected in size with the ordinary 

 spicules, only being specially short and thick, and in contrast to the case in the preceding species they 

 are here shorter than the ordinary dermal spicules. So far as I have seen, these thicker spicules are 

 found in the outer part of the fibres, just at the dermal membrane, b. Microsclera; these are chelae 

 arcuatse; they have a strongly, sometimes semicircularly curved shaft, the alse are lobe-shaped, and 

 short and round; the length is 0-028 0-037 mm , the most strongly curved may sometimes be a little 

 shorter; the shaft is somewhat flattened, its thickness is in accordance herewith 0-004 0-007 mm ; 

 developmental stages were seen in small numbers. The chelae are seen through the whole sponge, 

 but only in small numbers, in the dermal membrane they form on the other hand a more or less 

 dense layer, and they are numerous in the pore-membrane. 



This species is rather similar to and seems also nearly related to //. occulta, but it is charac- 

 teristically distinct; as to the skeleton it is distinguished by the absence of a proper dermal skeleton, 

 and with regard to the spicules the chelae have a different shape and are much more curved; also the 

 difference in the development of the dermal spicules with diactinal beginning in one and monactinal 



