338 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM. 



it he derived D. ingalli and from the latter D. japonica. This 

 grouping of Lindgren's is open to the criticism (Thiele, 1900, Dendy, 

 1905, 1916, Hentschel, 1909, 1912) of being artificial, in that the 

 characters of the smaller euasters are exclusively used for the dis- 

 tinguishing of species, although other points of difference between 

 recorded forms are known and again there are recorded forms 

 which, in respect to the astrose characters, are intermediates, falling 

 not in but between Lindgren's species. 



Thiele (1900, p. 61) points out that for the secure foundation of 

 the species it is essential to learn how constant within a species is the 

 structure of the cortex. 



Dendy in 1905 (p. 113) was inclined to use the well known, widely 

 spread, and manifestly variable form, D. lyncurium Authors 

 (Mediterranean, Atlantic, and Arctic Oceans) as a world-wide 

 species, and recorded Ceylon forms under it as varieties. Later 

 (1916, p. 260) he refers these eastern forms to D. japonica, D. 

 ingalli, and D. seychellensis, adding a new species, D. stella-grandis, 

 distinguished especially by the very large size of the spherasters. 



Hentschel, 1909, would disregard the difference in cortical 

 anatomy recorded for D. seychellensis and for D. ingalli, merging 

 the former in the latter. Topsent (1897, 1906, 1918) practices this 

 treatment. In 1912 (p. 316) Hentschel decides for a use of the 

 designation D. ingalli as covering a group of forms, " species, sub- 

 species, tropi," which it is not at present possible to characterize 

 differentially. Such conclusions state, implicitly at least, a task of 

 systematic zoology that begins to be imperative — namely, the criti- 

 cal study of certain widely spread and variable species, with the 

 purpose of marking out the lines and magnitudes of the varia- 

 tion that affects, in different quarters of the world, the several " char- 

 acters," setting down also the environmental conditions that are 

 associated with particular character combinations — all, as solid and 

 wide bases for rational experimentation. 



Topsent in his comprehensive and very helpful review (1918) 

 of the various forms (34 species and about 10 varieties) classed un- 

 der Donatia, proposes to merge many of them. I am here only con- 

 cerned with a few of the changes proposed. With regard to others 

 I have formed no opinion. Topsent would unite a number of 

 Sollas's types, D. ingalli, D. maza, D. seychellensis, D. nvaltijida, 

 along with several species more recently described, all under the 

 name of D. diploderma (Schmidt). In the matter of the name 

 chosen, it seems to me that Schmidt's description of Tethya diplo- 

 derma (1870, p. 52) is too incomplete to enable one to refer, with 

 certainty, specimens of Donatia to this species. Schmidt to be sure 

 states (1880, p. 78, footnote) that Selenka's T. maza (redescribed,' 

 from authentic specimens, by Sollas, 1888) is identical with hi* 



