32 THE VOYAGE OF H.M.S. CHALLENGER. 



Family II. Psamminidj;, Lendenfeld (PI. VII.). 



Definition. — Keratosa without spongiu-fibres. Pseudo-skeleton composed of xenophya 

 (or manifold foreign bodies), which are cemented together and enclosed by the transparent 

 maltha. Canal -system vesicular, developed on the Leuconal-type (similar to that of the 

 Spongelidae). 



The family Psamminidaa comprises those Keratosa (or rather " Pseudo-Keratosa ") 

 in which no trace of spongin-fibres is developed, the skeleton being composed only of 

 manifold foreign bodies, which are enclosed in the maltha or the mesodermal ground- 

 mass of the connective tissue. Lendenfeld, who founded this family in 1886 (as 

 Psaniminae, a subfamily of the Spongelidae), gives the following definition of it : — " The 

 skeleton consists of foreign bodies cemented by spongin, which, however, is not distinctly 

 visible ; without flesh spicules." 1 Three genera are distinguished by him, Psammo- 

 jyemma, Psammella, and Holopsamma. PsammeUa (Lendenfeld) has not yet been 

 described. The first genus, Psammopemma, described by Marshall in 1880, was placed 

 by him in the family Spongelidae or Dysideidas. I think, however, that the complete 

 absence of a horny spongin -skeleton is quite sufficient to separate the Psamniinidae from 

 the Spongelidae. No trace of true spongin or horny substance is to be found either in 

 those species described by Marshall as Psammopemma in 1880, nor in those described 

 by Carter as Holopsamma in 1885. Both these genera are represented by several new 

 deep-sea forms in the Challenger collection, and it contains besides three new species of 

 a new interesting genus, Psammina, the discoidal body of which is remarkable for its 

 simple structure. 



The Psaruminidae must be separated from the true Spongelidje for the same reason as 

 the Halisarcidae and Chondrosidae. They are indeed — regarded critically — skeletonless, 

 like the two latter families ; for the impregnation of the mesoderm with manifold 

 xenophya, or hard foreign bodies, produces only a pseudo-skeleton, — a solid supporting 

 mass in a physiological sense,— but not to be compared with a true internal skeleton 

 produced by the mesodermal connective tissue itself, as is the case in the Keratosa 

 proper. It would, therefore, perhaps be better to separate the Psamminidae as " Myxo- 

 spongiae arenosae," or Psanimospongiae, from the true Keratosa, and to unite them with 

 the skeletonless Myxospongiae (Halisarcidas and Ckondrosicke). 



Dr. N. Polejaeff, in his Eeport on the Keratosa, 2 describes two species of Psam- 

 mopemma collected by the Challenger in shallow water. The first is the form illustrated 

 by Marshall (Psammopemma densum), dredged at Station 49, in 85 fathoms ; the second 

 is a new form (Psammop>emma porosum) 3 found at Bahia in shallow water. Dr. 

 Polejaeff gives the following definition of Psammopemma: — " Spongelidaa without any 



1 Lendenfeld, Classification of Sponges, Proc. Zool. Soc. Lond., p. 589, Dec. 21, 1886. 



2 Zool. Chall. Exp., pt. xxxi. 2 hoc. cit., pp. 45-50, pi. iii. figs. 3, 4. 



