148 CEYLON PEARL OYSTER REPORT. 



and <}i'lli<Hh>s simply by loss of microscleres, the horny fibre being already strongly 

 developed in those genera, while others have probably arisen from Reniera and 

 Pftrosia simply by strong development of the horny fibre, the microscleres having been 

 already lost. 



The excessive development of spongin appears to have taken place independently 

 in many genera, and this fact, coupled with the loss of the characteristic microscleres 

 and the uniform character of the megascleres, renders it extremely difficult to arrive at 

 a natural classification of the Chalininae.* The subject is, however, much too complex 

 to be discussed here at length, especially as there are not a very large number of 

 species in the collection. For our present purposes it will suffice to make use of the 

 established genera, Pachychalina, Chalina, Ceraochalina. and Siphonochalina, 

 without committing ourselves to an expression of opinion as to their genetic relation- 

 ships. Owing to their degenerate character, it is impossible to define even these in 

 such a way as to distinguish them quite sharply from one another. 



Pachychalina, SCHMIDT. 



Chalininse of various external form, lobose or digitate, not tubular ; with stout 

 skeleton fibres, containing very numerous well developed spicules arranged 

 multiserially. 



Pachychalina subcylindrica, u. sp. Plate X., figs. 1, 2. 



Sponge elongated, rather slender, irregularly cylindrical or angular, probably 

 branched and repent. Surface fairly smooth but uneven, with a very few coarse 

 aculeations ; minutely reticulate to the naked eye. Vents fairly large (about 

 2'25 millims. in diameter), irregularly scattered, with slightly prominent margins. 

 Colour (in spirit) light brown. Texture compressible, resilient, rather coarsely fibrous, 

 but somewhat fragile. The largest piece measures about 95 millims. in length, with a 

 very variable thickness up to about 9 millims. 



The main skeleton is a sub-rectangularly meshed network of very stout multispicular 

 fibre, about 0'066 millim. in diameter ; with meshes varying greatly in size, and with 

 numerous spicules scattered irregularly between the fibres. The fibres themselves 

 contain a very large number of spicules, but no visible spongin. The dermal skeleton 

 (Plate X., fig. 1) is an irregular, polygonal- meshed network of similar coarse multi- 

 spicular fibre. 



Spicules. Oxea (Plate X., fig. 2) ; more or less curved or angulated ; when fully 

 developed stout and very sharply pointed at each end ; measuring about 0'L4 millim. 

 by O'OOS millim. Numerous slender forms also occur, probably immature. 



In the feeble development of the spongin this species occupies an intermediate 

 position between the genus Pctrosia and the more typical Chalininse. 



K.N. 292 ; 360 (Stat. II., north of Negombo, 9 fathoms). 



* Compare LKXDEXFKI.D (51) and DENDY (63). In the paper referred to I have explained the reasons 

 why I cannot accept LK\T>K\FKI.V>'S classification of the Chalininiie, 



