CLASSIFICATION III 



was proposed under a misapprehension of the rather obscure genus Gasacrinus, 

 which is a Camerate crinoid with biserial pinnulate arms, as has been proved 

 by excellent undescribed material since discovered. 



In 1902, 1 having discovered the presence of the radianal in Sagenocrinus 

 and Temnocrinus, I suggested a tentative arrangement of the Flexibilia into 

 two families, Ichthyocrinidae and Taxocrinidae, based upon the general form 

 of the crown, and the character of the arms, whether contiguous or divergent. 



Special study of this group with a view to the present work resulted in the 

 acquisition of material information regarding the true structure of hitherto 

 obscure genera, as well as newly discovered characters in others, and a pre- 

 liminary notice of some of these results was given in 1906. 2 The discovery of 

 the radianal in IcJithyocrinus, hitherto supposed to have a perfectly pentamer- 

 ous calyx, and in certain Taxocrinoid forms; of the actual relations of the 

 Silurian genera Anisocrinus, Clidochirus, Homalocrinus and Calpiocrinus; and 

 of certain definite modifications of characters from Silurian to Carboniferous 

 time; led to a considerable increase in the number of genera, and to a more 

 logical basis for their arrangement into families. A further tentative classi- 

 fication was proposed, by which the group was divided into three families, 

 Ichthyocrinidae, Sagenocrinidae, and Taxocrinidae, based primarily upon far 

 reaching differences in the anal structure, and secondarily upon the degree of 

 contact or separation of the rays due to the presence or absence of interbrachial 

 plates. 



Continuation of my researches since that time has brought further in- 

 crease of knowledge, by means of which the subdivisions of the group, while 

 in general features similar to those of 1906, are placed, as it is hoped, upon a 

 sounder basis. The following definition is believed to express the results of 

 all the evidence tending to establish the Flexibilia as a morphological unit : 



1 American Geologist, vol. 30, pp. 88-97. 

 3 Journal of Geology, vol. 14, pp. 467-523. 



