THE 



JOURNAL OF GEOLOGY 



SEPTEMBER-OCTOBER, 1906 



DISCOVERY OF THE DISK OF ONYCHOCRINUS, AND 



FURTHER REMARKS ON THE CRINOIDEA 



FLEXIBILIA 



FRANK SPRINGER 



East Las Vegas, New Mexico 



The Disk of Onychocrinus 



In the year 1888 Wachsmuth and Springer^ published their "Dis- 

 covery of the Ventral Structure of Taxocrinus,'''' based upon a remark- 

 able specimen of T. intermedius from the Kinderhook group of the 

 Subcarboniferous, at Le Grand, Iowa. Until that time nothing what- 

 ever had been known concerning the structure of the tegmen in the 

 Crinoidea Flexibilia; but numerous theories about it had been dis- 

 cussed, all of them based upon the assumption that it was in the 

 nature of a closed vault analogous to that of the Camerata, and sup- 

 posed to be common to all the paleozoic Crinoids. The specimen 

 above mentioned, however, demonstrated that in Taxocrinus, and pre- 

 sumably in the Flexibilia generally, the tegmen had an open mouth, 

 surrounded by five oral plates, with ambulacra passing in between 

 them, after the manner of the Recent Crinoids. This interpretation 

 has been accepted by all subsequent writers, and our figure of the 

 tegmen of Taxocrinus has been copied in almost every treatise on 

 Crinoids or general paleontology published since that time. 



In that paper it was stated that traces of alternating ambulacral 

 plates had been seen in a specimen of Onychocrinus, but not the orals, 



I Proceedings, Academy of Natural Science, Philadelphia, November, 1888, p. 337. 

 Vol. XIV, No. 6 467 



