RETEOCRINID^ . 177 



Distribution. — Age of the Trenton and Hudson river groups. Eestricted 

 to America. 



Remarks. — According to Billings, the calyx of Reteocrinus stellaris, the 

 type of the genus, consists of a reticulated skeleton, composed of incomplete 

 or rudimentary plates, each consisting of a central nucleus, with three to 

 five stout processes radiating from it. Of such plates he describes three 

 rings of five each, corresponding in position with infrabasals, basals, and 

 radials of other Crinoids, and he states that the genus in general structure 

 agrees with Cyathocrinus^ Dendrocrimis, and allied forms. 



It w^ould seem at first sight that this description does not apply to 

 '^ Glyptocrinus'' Onealli and the other species that have been referred to this 

 genus, as they have numerous interbrachials and interdistichals which Bil- 

 lings failed to notice. These plates, however, are actually present in the 

 type specimens, having been exposed by additional cleaning. Looking at 

 Reteocrinus Onealli in its usual preservation, with its deep interradial areas 

 covered by matrix, it corresponds well with the original description. The 

 specimens in that state seem to have but three rings of plates in the calyx, 

 and free brachials from the radials up. 



Miller refers to Reteocrinus only Billings' two typical species, placing the 

 other three under Gaurocrinus. We cannot discover any ground for generic 

 separation of the Ohio and Canada species. It is true Reteocrinus stellaris has 

 a third costal, but Miller himself did not attach much importance to this 

 character, for he grouped Reteocrinus fimhriatus with but two costals, along 

 with R. stellaris, which has three. 



In amending the genus Reteocrinus in 1881,* we referred to it the follow- 

 ing species : Glyptocnnus Baeri Meek, Glyptocrinus cognatus Miller, Reteocrinus 

 fimhriatus Billings, Reteocrinus gracilis Wetherby, Glyptocrinus Onealli Hall, 

 Glyptocrinus Richardsoni Wetherby, and Reteocrinus stellaris Billings. We 

 afterwards f withdrew Reteocrinus Baeri, which we found to be a Xenocrinus, 

 and Reteocrinus Richardsoni, which we placed under Canistrocrinus ; and we 

 added Gaurocrinus magnificus S. A. Miller. Reteocrinus cognatus is probably 

 a large R. Onealli, and E. gracilis a synonym of Ptychocrinus parvus. 



* Revision, Part II., p. 192. 

 t Revision, Part III., p. 96. 



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