PORIFERA. III. 



beginning in the other species is to be noticed. - I think it very probable, that the specimens 

 mentioned by Topsent (1. c.) from stations 600 and 899, and which the author refers with some doubt 

 to H. occ^ilta, belong to the present species, as he declares the spicules to be somewhat smaller, and 

 especially as he observes, that the chelae are more curved than in the typical occulta ; his figures 

 belong on the contrary certainly to occulta. 



Locality: Station 9, 64 18' Lat. N., 27 oo' Long. W., depth 295 fathoms; station 54, 63 08' Lat N., 

 1 5 40' Long. W., depth 691 fathoms; station 85, 63 21' Lat. N., 25 21' Long. W., depth 170 fathoms; 

 station 98, 65 38' Lat. N., 26 27' Long. W., depth 138 fathoms; further it has been taken East of the 

 Faroe Islands, depth 250 fathoms (Ad. Jensen, the cruise of "M. Sars" 1902), at 66 20' Lat N., 25 12' 

 Long. W., depth 96 fathoms (Wandel), and at Angmagsalik in East Greenland, depth 140 fathoms (The 

 Amdrup Expedition 1900). The localities are situated at East Greenland, West and South of Iceland 

 and East of the Faroe Islands; the bathymetrical range goes from 96 to 691 fathoms. 



If the species mentioned by Topsent with more curved chelae and smaller spicules should 

 prove to be the present species, it has also been taken at the Azores in depths of 185 and 106 fathoms. 



Remarks: The two species H. occulta and simillima show great resemblance, and they might 

 be thought nearly related if it were not for the difference in the manner of development of the 

 dermal spicules. The existence of this difference is very interesting, but it is not, however, possible 

 to decide for the present its real importance. --- The occurrence of special dermal spicules besides the 

 ordinary ones is also an interesting fact; these spicules seem to be only extreme variations of the 

 ordinary form, and we have then here again a fact, showing that the spicules placed outermost in the 

 sponge may be liable to special variations, such as I have pointed out more particularly in Part II of 

 this work (p. 32 33); also the difference in the abundance of these spicules in different specimens 

 of the same species, as shown by occulta, has its parallel, as mentioned at the place cited. 



23. H. baculifera Tops. 



PI. VIII, Fig. i. 



1901. Leptosia baculifera Topsent, Arch, de zool. exp. et gen. 3, IX, 354. 



1904. Topsent, Resultats des camp. sc. du Prince de Monaco, Fasc. XXV, 191, 



PI. XV, fig. 2. 



Incrusting; surface without projecting spicules. Spicula : rnegasclera ; the skeletal spicules acantho- 

 styli with a distinct head-swelling, spined in the whole or nearly the vahole length, 0-077 0-214""", not 

 divided into two groups; the dermal spicules strongyla varying to subtylota ovj 0-238""*; microsclera 

 small chela arcuata- 0-021 0-025""". 



This species forms very thin incrustations on stones and on tubes of Placostegus tridentalns 

 and other serpulid tubes. The greatest extent to which any of the specimens reach is 38 mm , and 

 the thickness is about 0-3 ram . The colour (in spirit) is whitish to brown. The surface has no projecting 

 spicules, but seen with a lens it is finely gritty, caused by the skeletal styli. The dermal membrane 

 is a thin film, it is filled with microscleres and supported by dermal spicules. Oscula and pores I was 

 not able to detect. 



