PORIFERA. I. 



55 



seen, which shine through as winding and branching lines, and which I take to belong to the incur- 

 rent system. Vosmaer, I.e., takes the regular arrangement of the canals to be characteristic of tlie 

 genus, which is also rather probable, but, strange to tell, it has not been mentioned b\- the later authors. 



This species not unfrequently shows a tendency to separate into concentric layers, not only 

 the skin, but also a series of layers in.side the skin scaling off easily; this feature, perhaps, may be 

 connected with the arrangement of the canals. 



The pores are found in the meshes of the dermal reticulation, and have a size of O'oS — o-ij'"'". 



The skeleton consists of a more or less regular network of fibres; the fibres appear chiefly to 

 have two directions, running towards the surface, and parallel to the surface. Generally the fibres 

 running parallel to the surface, are the more distinct ones. The fibres contain rather many spicules, 

 and have a thickness of about o-i'""'; the meshes may be much varying in .size, but most frequently 

 they were measured to a size of 0-45'"™. Outside of the fibres spicules occur scattered in every direction, 

 but these spicules are all shorter and finer than those forming the fibres. Spongin is present, but 

 onh' to a very small amount; it is only seen here and there uniting the ends of the spicules. As be- 

 fore mentioned, a close reticulation of meshes is found in the skin, the meshes of which are on an 

 average considerably smaller than those of the other parts of the skeleton; outside of this network 

 are moreover found scattered smaller and finer spicules of the same size as those occurring in the 

 sponge outside of the fibres. 



Spiaila are oxea; they are evenly, sometimes somewhat irregularly curved, of equal thickness 

 through their whole length, and rather abrupth" pointed. Their length varies between o-o8— o^s™"'. 

 Although all transitions between these sizes ma\- be found, the intermediate sizes are so scarce that 

 the spicules may be said to divide into two groups that are also of different occurrence in the sponge. 

 The large spicules have a length of about o-2— 0-35'™, but by far the most frequent size is 0-3™™; the 

 thickness is 0-017™"'; these spicules form the skeletal fibres and the dermal reticulation. The small 

 spicules on the other hand, occur scattered in the skin, outside of the reticulation proper, as well as 

 throughout the sponge scattered in the tissue outside the fibres; they reach a length of up to o-iy""", 

 and the)' are comparatively finer than the large ones, of an average thickness of 0-007""", but the two 

 groups, as has been mentioned, are not quite sharply separated. Besides these spicules not a small 

 number of .small, short and thick, curved oxea and strongyla may be found, and also other different 

 forms (PL VII, fig. 5 c). 



This species seems to be closely alhed to P. dura Nardo, but it is distinguished from the latter 

 species b\- its longer spicules (the spicules of a specimen of P. dura in the museum of Copenhagen 

 measure 0-26"™); moreover, its fibres are not by far so thick or consist of so man\- spicules as the 

 fibres of P. dura. 



Locality: Station i, 62= 30' Lat. N., 8° 21' Long. W., depth 132 fathoms, 16 specimens. 



Geogr.distr. Carter, I.e., has the species from about the same locality, that is, a Httle south 

 of the Faroe Islands, depth 167 fathoms (Porcupine ). The occurrence of the species on this latitude 

 is rather interesting, the genus not being hitherto known as northern, but only from the Mediter- 

 ranean and more southern regions. 



