PORIFERA. III. 75 



Of this species only one very small specimen is present, growing as an incrustation on the 

 inside of a Pecten-shell] it is longish and has a greatest extent of only 3*5 ram . The colour (in spirit) 

 is whitish. The dermal membrane is thin and densely filled with chelae. Oscula and pores were not 

 observed. 



The skeleton. The dermal skeleton consists of bundles and spicules, which are scattered in 

 different ways from near the base to the dermal membrane; it seems to be rather diffuse; there is no 

 skeleton of dermal spicules lying horizontally in the dermal membrane, but this latter is densely filled 

 with chelse. The main skeleton seems to be somewhat slightly developed, it consists of acanthostvli 

 which are all of the same size, and have the heads based on the substratum. I could detect no 

 spongin. 



Spicula: a. Megasclera. 1. The skeletal spicules are very slightly spined, almost smooth 

 acanthostyli; they are straight or slightly curved and have a slightly inflated head; this latter bears 

 more or fewer, but generally only few small spines; near the head the style may be very finely 

 gritty, but for the rest it is quite smooth. The styli are only of one form and very slightly varying 

 in size, so that small forms do not occur. The length is about 0-44 — 0-48 mra , and the thickness of the 

 head is about 0*017 mm . 2 * The dermal spicules are tylota, which are straight, slightly thickened in 

 the middle and with small end-swellings; these latter may be very small or absent, the spicules thus 

 becoming strougyla; the length is 0-27 — o*34 ram and the thickness in the middle 0*005 — 0*007 mn *. b. Micro- 

 sclera; these are chelse arcuatse; they have a rather curved shaft which is a little recurved at the 

 outermost extremities, the alae are lobe-shaped and the tooth narrowly elliptical; the length of the 

 chelse is 0*045— 0*052 mm , anc - the thickness of the somewhat flattened shaft is 0*005— 0*008 mm . The chelse 

 occur in specially large numbers in the dermal membrane. 



This species is easily distinguished and stands somewhat apart on account of its almost smooth 

 styli, which are all of nearly the same length. 



Remarks: It might be thought, that this species represented only a young stage of some other 

 sponge (a Lissodendoryx\ but I do not think this possible. To be sure we have no investigations on 

 the skeleton of the youngest fixed stages of the sponges which may come into consideration here, 

 and it is therefore not known, what the first beginning of the skeleton is in species with a reticulate 

 or dendritical skeleton, and it is not impossible, that the styli may at first be placed vertically. The 

 structure of the present species seems so fully to conform with that of Hymedesmia, however, that I think 

 it must be in reality & Hymedesmia; the styli with a somewhat distinct head, and especially the chelse 

 being crowded in the dermal membrane are good characters of Hymedesmia. 



Loeality: Station 89, the Denmark Strait, 64" 45' Lat. N., 27 20' Long. W., depth 310 fathoms. 



27. H. Bowerbanki n. sp. 

 PI. Ill, Fig. 8 a, PI. VIII, Fig. 5. 

 Incrusting, thin; surface smooth. Spicula: megasclera ; the skeletal spicules short, club-shaped, 

 strongly and entirely spined acanthostyli oj One size <rog — o-ij""" : the dermal spicules tylota 0-19 — 0-238"""; 

 microsclera chela- arcuatce 0-020 — 0-034""". 



