152 Clark — Tiro New Crinoid Genera. 



E. siboga ( Doderlein ). 



E. wyville-thomsoni ( Wyville-Thomson). 



Hypalocrinus gen. nov. 



Genotype. — Pentacrinus naresianus P. II. Carpenter, 1882. 

 A genusof Pentacrinitidae in which the first two post-radial and first two 

 post-costal joints are united by synarthry; a single interpolated series is 

 present; no further division; the first oblique muscular articulation is 

 between the second and third brachials beyond the only axillary ; infra- 

 basals?; basals as in Endoxocrinus, and not narrow, forming a rounded 

 stellate figure, as in Isocrinus. 



Geographic distribution. — Kermadec Islands, Fiji, Celebes, and I *1 ii lij >- 

 ] >ines. 



Depth.— 500-1350 fathoms. 

 The only known species is: 



H. naresianus (P. IT. Carpenter). 

 The species remaining in Isocrinus as here restricted are (in addition to 

 numerous fossil species): 



I. (Cenocrinus) asteria (Linnaeus). 



/. (Isocrinus) blakei (P. H. Carpenter). 



I. (Isocrinus) decorus (Wyville-Thomson). 



si x-ray I'd, while the numerous species of the same genus within t In • normal tropical area 

 are invariably five-rayed, and the most variable species of Metacrinus, M.rotundus, is 

 also tin' most northerly of the genus; it is the same with species; the examples taken 

 farthest from the center of distribution, or at the limits of distribution, are the most 

 variable; Tropiomt tra carinata, corstanl in its characters from Kast Africa to< Oceania, is 

 extremelj variable in Brazil; Antedon bifida is more variable about the British coasts 

 than in the Mediterranean, and Heliometra eschrichtii varies most along the southern 

 limit of its range. 



