SILICIOUS AND HORNY SPONGES WILSON. 467 



A second dried specimen (pi. 13. fig. 8), precise locality unknown, 

 is of the lamellate type. The skeleton shows a radial striation, ab- 

 sent in the other and which is not mentioned in the literature of the 

 species. It is in all probability correlated with the arrangement of 

 the larger canals, neither feature being fixed (hereditary). In order 

 to call attention to this, physiological, peculiarity, the sponge may 

 be designated forma striata. 



The lamella is 130 mm. wide, 75-90 mm. high, 1.5 mm. thick; one 

 face slightly concave, the other slightly convex. Concave surface 

 vaguely undulating, the undulations parallel to the free edge. On 

 each surface there are thickly crowded minute apertures, about 150 \l 

 in diameter. The oxeas are smaller than in the other specimen, 

 measuring only 210-300 by 3-1 y.. 



The skeleton shows on the surface, especially after boiling for a 

 few minutes in nitric acid, fine lines that radiate from the base of 

 the lamella toward the free margin. This radiate arrangement which 

 is visible to the eye exists throughout the interior, as may be seen in 

 tangential sections. The appearance is directly caused by the fact 

 that along lines which are roughly radial, the desmas lie much closer 

 together and are united in a more complex fashion than in the inter- 

 vening areas. Except in this feature there seem to be no differences 

 from the skeletal framework of the other specimen. 



Holotype.— Cat. No. 21321, U.S.N.M. 



Appendix to Leiodermatiidae. — Forms with sigmas. 



Microscleroderma Kirkpatrick (19026, p. 173) and Taprobane 

 Dendy (1905, p. 102) may conveniently be listed here. M icrosele ro- 

 derma is assigned by its author to the Scleritodermidae, although it 

 lacks the ectosomal rhabds of this family. Kirkpatrick would over- 

 come the difficulty by interpreting the rhabds in question as modified 

 and large sigmas. But the rhabds of the Scleritodermidae can 

 scarcely be claimed as microscleres, since they measure 80 to 540 [/. in 

 length, and it seems very doubtful whether there is- any real resem- 

 blance to sigmas. The size, radiate arrangement, and tylote outer 

 end of the spicules in species of Aekulites suggest, on the contrary, 

 the thought that they may even be degenerate triaenes. Perhaps 

 observations on the variation of the rhabds, including monstrous 

 forms, might throw light on their phylogeny. 



Taprobane, as Dendy (1905) has pointed out, would fall in the 

 Leiodermatiidae (indeed in Leiodermatium) were it not for the 

 presence of sigmas and, on the other hand, might be regarded as a 

 Scleritodermid without special ectosomal spicules, and thus there is 

 no place for it in Hollas' classification. The general evidence that 

 microscleres are easily lost is strong to-day. and for that reason I list 

 the genus in an appendix to the Leiodermatiidae, as above. If Sottas' 



