52 PLATYCRINID^. — HEXACRINUS. 



which we are convinced at one period existed. We have therefore no hesitation in 

 referring both the plates to the genus Hexacrinus. 



A similar obliteration of the divisions in the dorso-central plate of the Cyathocrinus 

 geomelricus has also been observed in specimens from the same system of rocks. 



Several fragments of columns have been obtained from the same localities as the 

 four species of Hexacrinl figured in plates 6 and 7, but we have been unable to 

 determine to what species they may be referred. Portions of four of these columns are 

 represented in plate 7. 



