PORIFERA. III. 



55 



ii. H. nummulus n. sp. 

 PI. Ill, Fig. ii, PL VI, Fig. 7. 



Incrusting ; surface hispid? Spicula: megasclera; the skeletal spicules acanthostyli with no real 

 head, divided into two groups, large, only spined below, 0-57 0-03""", small, entirely spined, 0-12 ai^ mm 

 the dermal spicules strongy la, somewhat tending towards tornota, o-jj 0-46 mm ; microsclera chela arcuatce, 

 strongly curved with the ends somewhat recurved, 0-028 0-034""". 



Two specimens of this species grow as small incrustations on stones, both of which are richly 

 overgrown with several other sponges, a third specimen coats the broken base of a Hornera sitting 

 on a stone. The greatest extent reached is only io mm . The colour (in spirit) is white. Beyond the 

 surface project the long styli, but whether this is so in the undamaged sponge I cannot say, as the 

 surface is in nearly all places not intact. The dermal membrane is a thin film and seems to have no 

 proper skeleton, but it is for the greater part wanting. Oscula and pores were not observed. 



The skeleton. The dermal skeleton; the dermal spicules form bundles stretching more or less 

 obliquely from the lower part of the sponge to the dermal membrane; the bundles are often rather 

 thick. The main skeleton consists in the ordinary way of acanthostyli with their heads placed on the 

 substratum; the long styli reach through the whole sponge; the small styli are by far the most 

 numerous, so that each of the large styli is placed in a group of small ones. Spongin is found at 

 the base of the styli. 



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

 two very distinct groups, large and small; the large styli have the base a little thickened but not 

 forming a real head, from here the style tapers evenly to the point; the base bears distinct, but not 

 large spines, outwards they soon nearly disappear so that about the lower half part is only slightly 

 gritty, the rest is smooth; the styli are generally somewhat curved near the base. The small styli 

 also have the head but little pronounced, but it is beset with somewhat large spines, and for the rest 

 the style is spined in its whole length, with somewhat reclined spines. The length of the large styli 

 is 0-51 0-95""" with a thickness at the base of 0-035 0-040 mm , the small styli are 0-12 o-i4 mm long 

 and at the base about o-O2i mm thick. 2. The dermal spicules are strongyla with some tendency 

 towards tornota; they are straight and generally one end is a little more pointed than the other; they 

 are of the same thickness in the whole length; their length is 0-35 0-46 ram , and the diameter 0-005 

 o-oo8 mm . Microsclera are chelae arcuatae; they have a strongly curved shaft, with the end-parts 

 somewhat recurved, the alas are lobe-shaped and the tooth elliptical; the chelae vary somewhat in 

 size, the length is 0-028 0-054 mm an ^ the diameter of the shaft is 0-004 o-oo6 mm . The mentioned 

 recurvation of the end-parts is very slight or quite disappears in the smallest chelae. 



This species bears some resemblance in spiculation to H. rugosa, but it has larger and much 

 smoother styli, smaller chelae of a different shape, and the strongyla are not polytylote; it is also 

 allied to //. stylata n. sp. (to be described hereafter), but differs by the longer and thicker acanthostyli, 

 and a different shape of the chelae which in stylata have the end-parts not recurved. 



Locality: Station 85, 63 21' Lat. N., 25 21' Long. W., depth 170 fathoms; station 89, 64 45' 

 Lat. N., 27 20' Long. W., depth 310 fathoms; and at 65 50' Lat. N., 26 53' Long. W., depth 



