PORIFERA. III. 



53 



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

 up to the membrane from the skeleton below, partly and chiefly of spicules lying horizontally in the 

 membrane; the latter spicules are partly scattered, partly collected into bundles or short fibres. The 

 main skeleton is formed of vertical acanthostyli, the shorter of which reach to the surface, while the 

 longer project through it. At the base of the acanthostyli there is found an amount of spongin, but 

 it is difficult to observe. 



Spicula: a. Megasclcra. i. The skeletal spicules are acanthostyli, they have the head-end 

 slightly swollen and taper from here into a long apex. The styli are divided into two sizes which 

 are to be sure not connected by transitional forms, but do not show, however, any principal difference 

 in shape. The larger styli are straight or slightly curved; they have a densely spined head, the 

 spines are here not pointed, but truncate or irregularly cut at the apex; on the lower part of the 

 shaft the spines are still somewhat dense, but they are small, outwards they become more scattered, 

 and the outermost part is smooth or has only some single spines; the spines on the shaft are reclined. 

 The small styli are likewise straight or very slightly curved, they are spined in the whole length, 

 and the spines are reclined; the head is most densely spined. The length of the large styli is 0-286 

 0-47 mm with a diameter at the head of 0-028 nim ; the greatest length is only rarely seen; the small styli 

 are 0-12 0-15""" long and o-O2O mm thick at the head. 2. The dermal spicules are straight strongyla, 

 one end is a little thinner than the other, and this thinner end is often slightly swollen; the length 

 is 0-238 o - 3i mra and the diameter about 0-004"'. b. Microsclera; these are chelae arcuatse; they 

 have an evenly curved shaft, an elliptical tooth and lobe-shaped alae of the same length as the tooth; 

 the free middle part of the shaft is not much more than the third part of the total length of the 

 chelae. The length is 0-032 0-037 mm , and the diameter of the shaft is about 0-004""". The chelae are 

 found in the dermal membrane, generally they are scattered, sometimes lying more densely. 



This species is distingushed from H. storea by its more slightly spinulous acanthostyli which 

 are divided into two groups, and by a different shape of the chelae. 



Locality: Station i, 62 30' Lat N., 8 21' Long. W., depth 132 fathoms; station 35, 65 16' Lat. N., 

 55 05' Long. W., depth 362 fathoms; station 98, 65 38' Lat N., 26 27' Long. W., depth 138 fathoms; and 

 East of the Faroe Islands, depth 250 fathoms (Ad. Jensen, the cruise of "M. Sars" 1902). The localities 

 are situated in the Davis Strait, the Denmark Strait and East and West of the Faroe Islands. 



10. H. similis 11. sp. 



PI. VI, Fig. 6. 



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

 but distinct head, the spinulation slight, the larger styli smooth in a long apical part, the styli divided 

 into two groups, large 0-41 o'6$ mm , small 0-149 0-238""*; the dermal spicules strongyla 0-298 o'jj""*/ 

 microsclera strongly curved chela arcuatce o-ojj 0-044 ""*. 



This species forms small incrustations on shells of Brachiopods, mussels and Gasteropods, and 

 on small stones; one specimen grows on a dead Oculina and another on a specimen of lotrochota 



