100 PORIFERA. III. 



They vary somewhat in size, the length from one hook to the other is 0-028 0-051 mm and the thickness 

 about o-ooio mm . The microsclera are especially found in the dermal membrane, the ordinary chelae 

 and the sigmata are however also seen throughout the tissue. 



As I have seen a preparation of the type-specimen, kindly sent to me from Professor Top- 

 sent, the determination is certain; as will be seen the shape and measurements of the spicules agree 

 very well, only the dermal spicules are different, but I think that Topsent's figure and measure- 

 ments are taken from non-typical spicules; the few dermal spicules present in the preparation sent to 

 me quite agreed with my figure (PL X, fig. 3 b) and were measured to 0-26 mm in length with a 

 diameter of 0-017 mm . 



Locality: Station 25, the Davis Strait 63 30' Lat N., 54 25' Long. W., depth 582 fathoms. One 

 specimen. 



Geogr. distr. Topsent (1. c.) has the species from 3755'L,at.N., 25 24' Long. W., depth 465 fathoms. 



44. H. tenuisigma n. sp. 

 PL X, Fig. 4. 



Incrusting; surface smooth. Spicula: megasclera; the skeletal spicules acanthostyli with a round 

 head, divided into two groups, large, only spined below, o-jo 0-8 j mm , small, entirely spined, 0-119 

 o-i6 mm ; the dermal spicules long strongyla 0-32 0-42"""; microsclera only sigmata which are large, but 

 thin, 0-084 o-i2 Mm . 



Of this interesting species we have two specimens, one growing on an Astarte-shell together 

 with H. le-uis, the other growing on a small Saxicava together with H. Koehleri and H. procumbcns. 

 The greatest extent to which the species reaches is about io mm , and the thickness is at most 0-6 ram . 

 The colour (in spirit) is brownish red. The surface seems, when the sponge is undamaged, to be 

 smooth. The dermal membrane is a thin film. Oscula and pores were not observed. 



The skeleton. The dermal skeleton consists of bundles of dermal spicules which stretch from 

 the skeleton below to the surface, they thus lie between the apical parts of the long skeletal spicules; 

 the spicules in the bundles are more or less penicillately spread outwards; the bundles are sometimes 

 rather large, consisting of many spicules. The main skeleton is arranged as usual and consists of 

 vertical acanthostyli, the longest of which stretch to the surface; at the base there is a small amount 

 of spongin. 



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

 two groups, large and small; the large styli are straight or, generally, slightly curved near the base; 

 they have a round, more or less swollen head and taper into a long and fine apex which generally 

 is a little more abruptly pointed outermost; the head-swelling is beset with medium sized, blunt spines, 

 and a short basal part has small spines, the rest of the style is smooth. The small styli are generally 

 straight, they have a round head-swelling which is however less distinct than in the large styli, it is 

 likewise beset with blunt spines, and the styli are spined in the whole or nearly the whole length, 

 but the spines are dispersed outwards. The length of the large acanthostyli is about 0-30 0-83 mm ; 

 they vary considerably in thickness from 0-020 0-029 mm and this has no relation to their length, the 



