SPONGES.-HALLMANN. 227 



be no question of the admissibilit}- ol their inclusion in one 

 species,^ one finds it impossible, with so few specimens, to form 

 any opinion as to whether they ought to be considered as 

 mere "metamps," or as representing two or three independent 

 varieties. For convenience of description I divide them into 

 four forms, distinguished as (a), (b), (c) and (d) respectively; 

 the first of these is chosen to represent the tvpical form. A 

 general description will first be given embracing the features 

 common to all, and then each will be described separately with 

 regard to the points in which it differs from the others. 



Geiienil Description. — The sponge is stipitate and more or 

 less ramose, with branches which, in general, are distinguished 

 into several successive 'orders of rapidly decreasing length ; in 

 some cases, owing to an excessive abbreviation of the branches 

 the habit might be described as sub-lobate. Anastomosis of 

 some of the branches usually occurs. There is, as a rule, a 

 rnore or less well-expressed tendency on the part of the deriva- 

 tive branches of one and the same branch to confine their 

 outgrowth to a single plane, and this tendency may sometimes 

 affect the entire sponge in a uniform way so that a flabellate 

 arrangement of the branches results. The most characteristic 

 external feature, and one which appears to be constant in oc- 

 currence, though variable in degree, is a nodular or warty 

 appearance of the surface, due to the presence everywhere of 

 short, rounded or slightly compressed outgrowths or processes. 

 In appearance and character these processes usually bear a 

 close resemblance to rudimentary branches ; and, indeed, it is 

 often difficult to distinguish between what on the one hand 

 should be regarded as incipient branches, and on the other, as 

 processes of larger size than usual. They are thus apparentl}- 

 quite of the nature of abortive branches. In some cases they 

 are so closely crowded that the intervals between them are 

 reduced to narrow sulci ; in others, they are sometimes widely 

 separated. Occasionally they take the form of short ridges. 



The dermal membrane is, at the best, only faintly developed, 

 and is usually indistinct. In the latter case the surface exhibits 

 a minute hispidity, due to the projecting terminal spicules of 

 the main fibres. This hispidity is most pronounced in the 

 typical specimen, in which the spicules are of greatest size. 

 There seems to be an inverse relationship between the degree 

 of hispidity of the surface and the degree of development of 

 the dermal membrane. 



The surface is closely though somewhat irregularly dotted 

 with small sub-dermal pores of slightly variable size which 

 are the more clearly distinguishable the less evident is the 

 dermal membrane. These pores appear frequently to be of 

 larger size when situated in the sulcar parts of the surface. 



