HIECINIA. 179 



expanding sponges, which attain a height of 300 millim. Specimens are often 

 met with which consist of an irregular erect basal mass, the margin of the 

 upper surface of which is extended horizontally or obliquely upwards so as to 

 form a disc or cup with very thick walls which thin out towards the sharp 

 margin. The basal mass is in other specimens much reduced in size, and 

 appears as a stout peduncle only ; such forms, however, are rare. More often 

 it happens that the whole sponge consists of a thin, curved, frondose, irregu- 

 larly flabelliform plate, which is attached by a long line at the base. The lateral 

 margins of this curved ear-shaped frond may meet and coalesce to form an 

 irregular calyculate structure. In these forms, which are usually large, the 

 walls of the cup are only 8-12 millim. thick, and much thinner and more 

 regular than in those of the first-mentioned series of forms in which a central 

 basal mass is observed. The surface is covered with conuli, arranged in more 

 or less regular longitudinal rows which appear as projecting ridges. The 

 conuli are larger on the outer convex than on the inner concave surface of the 

 lamellar parts, and also exhibit a diminution in number and corresponding 

 increase in size towards the base of the sponge. The longitudinal ridges are 

 2-3 millim. apart, the conuli 0-5-2 millim. high — according to their position — 

 and, in the ridges, on an average 1 millim. apart. The oscula are generally 

 confined to the inner surface, occasionally also found on the margin, but never 

 on the outer convex surface of the sponge ; they are 1-2 millim. wide, and 

 scattered over the concave surface, or arranged in groups of about 20, extend- 

 ing over an area 10-15 millim. wide. The colour of the living sponge is dark 

 dull red on the surface, and lighter, more yellowish in the interior. The dry 

 skeleton is dark brown and hard. 



The skeleton consists of radially situated columns of pretty closely packed 

 foreign bodies 0*2 millim. thick, attached to each other partly by continuous 

 masses of spongin cement, or by small isolated short and slender fibres, which 

 are on an average 0*03 millim. thick. These more or less perforated, or even 

 trellis-like main fibres are on an average 3 millim. apart, and joined to each 

 other by connecting-fibres 0'04 millim. thick. The latter form trellis-like 

 structures extending in the plane in which the main fibres lie, to which 

 they are attached. Halfway between the main fibres the connecting-fibres 

 form slender bundles, within which they approximate each other very closely, 

 being about O-06-O'l millim. apart. Between these bundles roundish meshes, 

 2-4 millim. wide, intervene. Towards the main fibres the connecting-fibres 

 diverge, the most diverging of the one extending to the joining-point of 

 the most diverging connecting-fibres of the next bundle. The filaments are 

 very abundant throughout the whole of the sponge; they are 0-01-0'014 

 millim. thick, and densely covered with brown spots on the surface. Bower- 

 bank's representation of these filaments (loc. cit.) is very good. 



Pretty abundant foreign bodies are found in the skin. The snbdermal 



n2 



