176 HIBCINIA. 



appears as a crust from the upper surface of which these processes arise. 

 Sometimes the crust is much curved, raised in the centre, attached at the 

 margin only, and perforated. According to the shape the following varieties 

 can be distinguished : — Incrusting or thicker and somewhat cake-shaped, 

 H. V. hh'suta ; massive, globose, with circumvallate oscula, H. v. Jlaves- 

 cens ; massive, globose, without circumvallate oscula, H. v. typica ; digitate, 

 branched, H. v. dendroides ; lamellar, raised in the centre, attached at the 

 margin, and perforated, //. v. galea ; thick, flabelUf orm, erect, H. v. lingua ; 

 with conic outgrowths, on each of which a terminal osculum is situated, H. v. 

 mammillaris ; and, finally, irregular, with rows of crateriform oscula, H. v. 

 oros. The surface is covered with rather blunt conuli, 1-2 millim. high, which 

 are 1-3 millim. apart. The dimensions and the shape of these conuli are often 

 subject to as great variations on the surface of one and the same individual as 

 on individuals of different varieties. Living sponges of this species appear to 

 have lower conuli than specimens preserved in spii'it, and the method of pi'e- 

 servation seems greatly to influence their appearance. The oscula are always 

 large and conspicuous. They are, in the case of the massi\'e and incrusting 

 forms, scattered over the upper surface, but always appear to be situated on the 

 summits of the protuberances of those varieties which have an uneven surface. 

 In the flabelliform B. v. lingua the oscula are situated marginally, and in S. v. 

 oros in rows on the summit of ridges which project from the surface. The 

 oscula are often circumvallate, and lie at the base of concave aconulous depres- 

 sions in the surface; this is particularly pronounced in H. v.fiavescens. In 

 certain forms of this variety — Hircinia dilobes, 0. Schmidt — groups of oscula 

 are often observed in these depressions. The oscula are 1-5 millim. wide. 



The colour of the living spouge varies from light to dark brown. This 

 colour is confined to a superficial layer 2 millim. thick. 



The sl-eletonis in all the varieties the same. The stouter main fibres attain a 

 thickness of 0-2 millim., are 1-2 millim. apart, and radiate from the base. 

 They are for the most part simple, but in places dissolved into a trelliswork- 

 like structure composed of slender fibres. Here and there they are flattened ; 

 but this peculiarity has, according to F. E. Schulze, not such an importance 

 as some authors, particularly Carter, who established a special group — Platyfihra 

 — for the horny sponges with flattened fibres, attach to it. The main fibres 

 are cored with foreign bodies, chiefly spicule-fragments, which are not very 

 abundant, and irregularly scattered. The connecting-fibres are generally 

 slightly branched, and attached to the main fibres by two or more roots ; very 

 scarce scattered foreign bodies are found in them here and there. The con- 

 necting-fibres are on an average 0*05 millim. thick ; the larger meshes of the 

 network which they form are about 1 millim. wide, and irregularly polygonal. 

 The filaments are, according to F. E. Schulze, 4-8 millim. long, and in the 

 centre 0-006 millim. thick ; towards the ends they gradually taper to 0*003 



