244 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



new genera and 1 a new subgenus. Two of the new species, Histo- 

 cidaris magnified and Goniocidaris (Discocidaris) peltata, are among 

 the most magnificent cidarids known. Each of them is represented 

 only by a single, fortunately very beautifully preserved, specimen. 

 The new genus Psilocidaris is especially interesting, being evidently 

 related both to the genus Aporocidaris and to the genus Goniocidaris 

 (in the broad sense) , and thus giving the clue to the true systematic 

 position of Aporocidaris, the affinities of which were hitherto rather 

 obscure. 



The number of species (and varieties) of cidarids, collected by the 

 Albatross in the Philippine seas, considerably exceeds that collected 

 by the Siboga from the whole of the Malay region which amounted to 

 18 (19) species. Only 9 species are represented in both collections, 

 while 18 species were taken only by the Albatross, as against 9 species 

 taken solely by the Siboga. As several species of cidarids not repre- 

 sented iD either the Albatross or the Siboga collections were taken by 

 the author, mainly at the Kei Islands (also one at the Philippines), 

 the total number of species of cidarids known from the Malayan and 

 Philippine seas already amounts to more than 40. Since several of 

 these are represented only by single specimens, it is safe to say that 

 our knowledge of the cidarids of this region is still far from complete. 

 We may well expect that a fair number of additional species will be 

 brought to light there by further investigations, so that the total 

 number of species of cidarids occurring in this region will very prob- 

 ably amount to about 50. Comparison between this number and 

 the 8 (perhaps 10) species of cidarids known from the West Indies 

 and 3 or 4 species known from the whole of the northeast Atlan- 

 tic very strikingly demonstrates how extraordinarily richly the 

 cidarids are represented in the Philippine-Malayan seas, evidently 

 more richly than in any other part of the world. 



