340 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



be. confused with true furcifer as the rays have an entirely different shape, and 

 the paxiUiB are more spaced. It is not possible to determine whether this form 

 figured by Grieg is a separate species or only a variation oi furcifer. At any rate it 

 must be considered separately hom. furcifer, and if the same as the race inhabiting 

 Bering Sea and the deptlis off northwestern North America, should be designated 

 as distinct iroin furcifer, the typical form of which appears not to be found in this 



area. 



Vexator may be a species which invades the Nortii Atlantic and which is quite 

 distinct from the resident furcifer. We seem to have to do with at least two dis- 

 tinct forms wliich range together to the north of Scandinavia. Even if vexator is 

 only a variety or "forma"- of /wrci/er, conditions are such that it is the type wliich 

 has survived in the North Pacific at lesser depths, and as it evidently intergrades 

 with furciUiger its name has been linked with that species rather than with furcifer, 

 with wliich intergradation is not demonstrateil. 



Family KORETHEASTERID^ Danielssen and Koren, 1884. 



Korelhrasleridse Danielssen and Koren, 1884; Bell, 1892; Gregory, 1900; Fisher, 1905. 

 Korelhrasterinx Sladen, 1889; Perkier, 1904. 



Spinulosa resembling supei-ficially the Solasteridae, but lacking actinal inter- 

 mediate plates, and with the armature of the adambulacral plates forming with 

 that of the inferomarginals a single transverse series, never webbed; inferomar- 

 ginals never paxilliform; interbrachial septa partlj' calcified; abactinal skeleton 

 composed of roundish plates, or lobed plates forming a wide mesh, bearing a tuft 

 of spinelets either independent or united by web; mouth plates plowshare-shaped, 

 resembling those of the Pterasterida;. 



Remarks. — This small family is usually placed under the Solasteridaj wliich it 

 resembles in respect to the abactinal skeleton and spinulation, but differs in lack- 

 ing actinal intermediate plates and in having the mouth plates of the Pteraster 

 tvpe, not the Solaster form. The armature of the adambulacral plates is also differ- 

 ent, being nearer that of the Pterasteridie, though entirely lacking a web. The 

 inferomarginals are never paxilliform as in the Solasteridae and Pterasteridse. 



The Korcthrasteridse seem to stand naturally between the Solasteridae and 

 Pterasterida;, combining a few of the characteristics of each family. The Solas- 

 teridae are more homogeneous if Peribolaster and Korethrasier are removed, for the 

 main likeness is to be found only in the abactinal skeleton. The reticulate structure 

 such as is found in Peribolaster and that of independent plates as in Korethraster 

 is paralleled in the Solasteridae, where the principal genera have a reticulate skeleton, 

 but Lxtmaster (olim Ctenaster) is more comparable to Korethraster, having the 

 abactinal platelets not united by intermediate ossicles or by their own processes. 



The structure of the actinal skeleton is more homogeneous, however, and is 

 distinctly nearer that of the Pterasteridae than of the Solasteridae, for the mouth 

 plates are of the characteristic Pteraster form and the actinal intermediate plates of 

 the Solasteridae are lacking. The inferomarginals are never paxilliform but bear a 

 prominent spine (or two spines) and are therefore different from those of the 

 Pterasteridffi. The adambulacral armature is more like that of Pteraster tlian of 

 Solaster. 



