304 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



tailed differentiation which they undergo, constitute, as I take it, the 

 really basic features. 



Genus ERYLUS Gray (1867). 



Erylus Gray, 1867. p. 549. 



The afferent orifices are uniporal apertures into chone canals; 

 efferent orifices also the uniporal openings of chone canals, or in other 

 cases larger oscula. The megasclere-complex includes orthotriaenes 

 and rhabds; anatriaenes and protriaenes absent. The sterraster is 

 more or less flattened, often so flattened as to be a thin plate. Micro- 

 rhabds (here spicules of good size, reaching a length of 70 jx), typi- 

 cally centrotylote, form a dermal layer. Euasters also occur, but not 

 at the surface. 



In some species the sterraster passes through an aspidaster stage, 

 a thin plate in which the first formed rays are completely soldered 

 together, thus giving the spicule for the time being smooth surfaces 

 and a smooth margin. The short rays which beset the adult spicule 

 develop secondarily upon the aspidaster stage. 



The sequence of changes made in Sollas's definition (1888, p. 209) 

 is as follows: 



In none of the recorded species, unless Stelletta intermedia O. 

 Schmidt be accepted as an Erylus (Sollas, 1888, p. 241), is the ster- 

 raster spherical, and Lendenfeld (1903, p. 85) emends by describing 

 the sterraster as " flattened, more or less disklike." 



Lendenfeld (1906, p. 305) adds that the sterrasters develop from 

 thin plates ("aus scheibenformigen Anlagen"). Lendenfeld at the 

 time does not rest this idea on direct observation of ontogenetic 

 stages, but on an examination of the adult sterraster. In E. yolyaster 

 he finds (p. 306) that the sterraster, which is only moderately flat- 

 tened, is concentrically stratified, the innermost part appearing as 

 a flattened plate which shows a radial structure, the surrounding 

 layers showing no signs of a radial structure. Lendenfeld regards 

 the inner, central, platelike mass as representing a young stage in 

 the development of the spicule (see also pp. 309-310). This account, 

 which is superseded by Lendenfeld's later one, of the sterraster 

 seems to imply that the spicule develops in a radically different way 

 from that presented in Sollas's scheme (1888, p. lxiv), in which 

 sterrasters in general are derived from spherasterlike stages through 

 growth and continued fusion, from the center outward, of the rays. 



Lendenfeld (1910&, p. 294) finds that the oscula are sometimes no 

 larger than the afferent apertures, and emends the definition accord- 

 ingly, saying the genus has " uniporal efferents or larger oscula." 



Lendenfeld (1910, p. 17; 1910&, p. 267) concludes as a result of his 

 discovery of actual ontogenetic stages that the sterraster of Erylus 

 is distinguished not only by its flattened shape but by passing 

 through a stage with perfectly smooth surfaces, which does not 



