IQ BULLETIN S2, UNITED STATES NATIONAL MUSEUM 



It will be noticed that the names of many of the new species described in this 

 paper occur as nomina nuda in the paper published on April 11, and that the family 

 Eudiocrinidae here accepted was in that paper shown to be untenable. This is 

 explained by the fact that the paper published on May 14 was written prior to that 

 published on April 11. , • . ^i 



For some time the author had been investigating the homologies of the post- 

 radial elements in the comatidids, and certain definite conclusions had been dra^vll 

 of which the most important was that the IBr and foUowing division series are in 

 reality nothing more than reduplications of the first two brachials interpolated 

 between the original first two brachials and the radials. This observation was 

 pubhshed in the paper containing the second installment of new genera formed 

 within the old genus Antedon as understood by P. H. Carpenter (AprU 11) in which 

 also the difference in arm structure between the type of Eudiocrinus indivisus and 

 E. japonicus is explained. Applying to the pentacriuites the facts discovered regard- 

 ing' the arm structure of the comatulids, it was at once seen that the genus Isocrimis 

 { = Pentacrinus as understood by Carpenter) was not a homogeneous entity, but is 

 made up of several distinct types. 



In a paper which appeared on June 9, 1908, the arm structure of the penta- 

 criuites was discussed in detail and compared with that of the comatulids. Two 

 new genera were proposed : 



Endoxocrinus (genotype Encrinus parrae Gu6rin [that is, Gervais], 1835 [ = Penta- 

 crinus miilleri Orsted, 1856]) including 



Endoxocrinus alternicirrm. Endoxocrinus sibogae. 



Endoxocrinus parrae. Endoxocrinus wyville-thomsoni. 



Hypalocrinus (genotype Pentacrinus naresianus P. H. Carpenter, 1882) including 

 Hypalocrinus naresianus. 



This leaves the following three recent species in Isocrinus: 



Isocrinus (Cenocrinus) asteria. Isocrinus (Isocrinus) blakei. 



Isocrinus (Isocrinus) decorus. 



It i? suggested that the young of Metacrinus will be found to possess 5 arms 

 only in contrast to the 10 arms of the young of the other recent pentacrinites. 



The species recorded by Reichensperger as "Pentacrinus decorus" in which he 

 figures the axial canals is redetermined as Endoxocrinus parrae. 



In, the diagnosis of Endoxocrinus the following statement is made: "infrabasals 

 always (?) absent, and interior ends of basals more or less resorbed, the primary 

 axial canals forking and entering the basals through two apertures." 



Endoxocrinus parrae, which inhabits the shallov/est water of any of the genus, 

 is extraordinarily variable, while the other species are pretty constant in their char- 

 acters; this is said to accord with the rule that a species of a genus which occupies 

 a habitat on the borders of the habitat of the genus as a whole, either geograpliically 

 or bathymetrically, is more variable than are the other species of the same genus; 



