PORIFERA. II. 



I 99 



Thickly incrusting or more massive. The surface slightly grooved. The dermal membrane a 

 thin film supported by most frequently highly recumbent bundles of dermal spicules. The skeleton a 

 quite irregular, polyspicular reticulation. Spicula: Mcgasclcra : the skeletal spicules styli 0-488— 0-62""". 

 the dermal spicules tylota 0-238— 0-309"""; m v< rose /era of four forms, isochelcr arcuatcr of two sizes, targe 

 ones 0-043 — 0-067""", small ones 0-021 — 0-028""", forcipes of two sizes, large ones 0-44—0-32""". small ones 

 0-028 — 0-036""". 



Of this species we have only one, highly damaged specimen, growing as a thick incrustation 

 on the carapace of a Hyas coarctatus, and a quite insignificant fragment. The specimen has a great- 

 est extent of $6 mm and a greatest thickness of 5 mn \ The specimens described by Bower bank and 

 Carter were of a similar form, bnt a little larger, having a greatest extent of respectively ca. 80 and 

 45 mm , and Carter's specimen having a thickness of fully I2 mm . The colour (in spirit) is gray. The 

 consistency is rather firm, but somewhat brittle and little elastic. The surface is slightly grooved, 

 the skeleton below causing small protuberances; otherwise it seems to be smooth. The dermal mem- 

 brane is a thin, transparent film, supported by bundles of dermal spicules. Pores were not seen on 

 my specimen. A few circular openings in the membrane I take to be oscula. Carter describes the 

 surface and the dermal membrane in the same way, but his specimen showed also the pores gathered 

 in sieves over the subdermal cavities. Also Bower bank mentions pores gathered into a group. 



The skeleton. The dermal skeleton consists of bundles of dermal spicules, issuing from the 

 skeleton below and supporting the dermal membrane; they are, however, very little projecting, but 

 highly, almost horizontally, recumbent; also scattered spicules are found here and there in the mem- 

 brane. The main skeleton is a polyspicular, but quite irregular network; meshes are formed, but they 

 have no definite form, and longer fibres are not formed. Here and there in the network single spi- 

 cules are found, but otherwise it is polyspicular. The number of spicules alongside may vary rather 

 much, most frequently it seems to be four to five, but it may also be greater, up to about ten. 

 Spongin is found in the nodes of the skeleton, but it is very white and clear. 



Spicula: a. Mcgasclera. 1. The skeletal spicules are styli; they are evenly and slightly 

 curved, the curve being most frequently found nearest to the rounded end; they are of about equal 

 thickness troughout the length, and the point is rather short, it is most frequently distinctly limited 

 and bounded by straight or almost straight lines. Their length is between 0-488 and 0-62""", rarely at 

 the lower limit. The thickness is from ca. 0-0128— 0-02 i mm . Developmental forms at different stages, 

 down to exceedingly fine ones, occurred rather frequently; the finest ones were long pointed. One of 

 the finest forms was 0'47 mm long. 2. The dermal spicules are tylota with slightly swollen ends; 

 sometimes the ends are so little developed, that the spicules approach strongyla; they are cylindric 

 and most frequently straight. Their length is 0-238—0-309""", and the thickness is ca. 0-004— o-oo57 n " n . 

 In the fully developed spicule the two ends are about equal, the shaft being at most a little thinner 

 in one end, and the swelling therefore a little more marked; the younger and finer the spicules are, 

 the greater is the difference between the ends, and the finest developmental forms seemed to have 

 one end pointed. Then the developmental forms show the peculiarity of being almost always poly- 

 tylote with a series of swellings along the shaft, which swellings dissappear by degrees, as the spicule 

 grows thicker, b. Alicrosclera; these are of four forms, two forms of isochelse areuaUe, large and 



