524 DR. A. GUNTHER ON A ZOOLOGICAL [JunC 23, 



IX. PORIFERA. 



By Arthur Dendy. 



Only a single Spouge was brought home by H.M.S. ' Flying-Fish,' 

 but this specimen is one of considerable interest. It belongs to 

 a new species of Schmidt's genus Pachychalina ^. It is only very 

 rarely that specimens of Chalinine Sponges come to hand in a 

 sufficiently well-preserved condition to allow of an investigation into 

 the structure of the soft tissues. Such investigation is likely to 

 prove of much importance in determining the true relations of this 

 large and difficult group of Sponges. Hence, as no account has 

 ever yet been given of the minute anatomy of any species of Pachy- 

 chalina, and, as indeed, only one or two Chalinine Sponges have 

 been anatomically described at all, I have thought it desirable to 

 give some description of the minute anatomy of the present species — 

 a proceeding rendered practicable by the excellent state of preserva- 

 tion of the specimen. 



Pachychalina spinosissima, n. sp. (Plate XLIV.) 



The single specimen in the Collection (Plate XLIV. fig. 1) consists 

 of a long, unbranched, irregularly cylindrical, repent stem, naturally 

 terminating at each end. The specimen has evidently been attached 

 by various parts of the lower surface to the sea-bottom. It is 

 covered all over with very large, stout, sharp-pointed, and often 

 branching spines (whence the specific name), and bears along the 

 upper surface a row of large oscula. Total length of specimen about 

 350 millim. (=14 inches); average diameter, exclusive of spines, 

 12 millim. ; average length of spines, 10 millim. Colour in spirit 

 brownish yellow. Texture compressible, elastic, tough, internally 

 cavernous. Surface subglabrous over and between the spines. 

 Dermal membrane (ectosome) very thin, delicate, and transparent, 

 reduced to a mere network by the very numerous pores (Plate XLIV. 

 fig. 2). Pores very numerous rounded openings, thickly scattered 

 through the dermal membrane, averaging about 0*05 millim. in 

 diameter (Plate XLIV. fig. 2). Oscula circular, pit-like openings, 

 having their margins flush with the general surface ; averaging in 

 diameter about 3 millim. ; arranged in a single series along the upper 

 surface of the sponge (Plate XLIV. fig. 1). 



Skeleton. — (a) Main : a coarse, irregular, wide-meshed reticula- 

 tion of stout spiculo-fibre, in which there is a strongly developed but 

 rather irregular system of fibres running more or less longitudinally 

 iu the direction of the long axis of the sponge. The fibres them- 

 selves are, as in other species of the genus, stout and polyspiculous ; 

 each consists of a stout spicular axis, composed of very numerous, 

 closely packed spicules hing side by side parallel with one another, 

 and a large proportion of spongin, which unites the spicules together, 

 and, generally at any rate, also forms a distinct sheath around the 



^ Vide Eidley and Dendy, Report on the Monaxonida dredged by H.M.S. 

 ' Challenger,' p. 19, for diagnosis and discussion of the genus. 



