1881.] NATURAL SCIENCES OF PHILADELPHIA. 253 



rays and the arms proper have been rarely observed, but were 

 apparent!}^ constructed like those of Eucladocrinus. In Hexacr. 

 limbatus, the free rays attain three or four times the length of 

 the bod}^, and each one consists of a row of short cylindrical 

 joints, which give off laterally pinnule bearing arms. These 

 arms originate on every fourth, fifth or sixth joint, according to 

 position, and alternately from opposite sides. The free parts of 

 the ray in Hexacr. brevis,^ are apparently more like those of 

 Plati/crinus. 



Anal plates generally narrower, but often higher than the first 

 radials; wider towards the top than at its junction with the 

 basals, the upper side supporting two or thi:ee plates. Inter- 

 radial series composed of a single large plate,, which rests within 

 a notch between two radials. 



Yault low, hemispherical, more or less flattened, composed of 

 comparatively few and large pieces, which are nodose, or covered 

 with a number of small tubercles. Apical dome plates large. 

 Anus subcentral or lateral ; in form of a simple opening through 

 the vault, or supported bj"- a small tubercular process composed 

 of small polygonal pieces. 



Column cj^lindrical, the larger joints nodose or sculptured after 

 the style of the plates of the calyx; articulating face radicularly 

 striated ; central canal small, round. 



Geological Position^ etc. — Hexacrinus is strictly a Devonian 

 genus, and almost exclusively European, only fragments of a 

 single species having been discovered in America. 



The following species have been described : — 



1838. Hezaorinas anaglypticos Goldf. (Platycr. anaglypticus.) Nova Acta ac. 

 Leop., xix, p. 348, PI. 32, fig. 4; Schultze, 1867, Hexacr. anaglypticus, 

 Mon. Echin. Eifl. Kalk, p. 72, PI. 8, fig. 1. Devonian. Eifel, Germany. 

 Syn. Platycr. frondosus Goldf. Bonn Museum, undefined. 

 Syn. Platycr. annulatus Goldf. Bonn Museum, undefined. 

 Syn. Platycr. muricatus Goldf. Bonn Museum, undefined. 

 1867. Hexacr. bacca SchuUze. Men. Echin. Eifl. Kalk, p. 83, PI. 10, fig. 5. Devo- 

 nian. Eifel, Germany. 

 1838. Hexacr. brevis Goldf. (Platycr. brevis.) Nova Acta ac. Leop., xix, i, p. 

 346, PI. 32, fig. 2; Schultze, 1867, Hexacr. brevis, Men. Echin. Eifl. Kalk, 

 p. 79, PI. 10, fig. 7. Devonian. Eifel, Germany. 



1 We believe that Hexacr. brevis Goldf. (Mon. Echin. Eifl. Kalk, PI. 10, 

 fi^. 7) is a young specimen of some other species. This is indicated not 

 only by its small size, but also the immature character of the anns and 

 column ; it may even represent an entirely different genus. 



