TAXOCRINIDAE 343 



This is the sole family of the suborder Taxocrinidae, and its chief charac- 

 ter is the weak calyx with anal tube originating on the posterior basal, as fully 

 explained in the chapter on Classification. Associated with this character is the 

 usually elongate crown, of which the rays are always partly or wholly separated 

 above the radials by interbrachial plates or perisome; and the arms are usually 

 more or less divergent. There is no genus of this family with completely inter- 

 locking rays such as are found in the Lecanocrinidae and Ichthyocrinidae, and 

 only one, Parichthyocrinus, in which they abut or interlock at all. That genus 

 has a decidedly different facies from the others of the family, and upon the 

 ground of superficial resemblance might well have been placed among the 

 Ichthyocrinidae, towards which it also tends in the frequently reduced size of 

 the inf rabasals. It is an intermediate type, and belongs among the Taxocrinidae 

 as now understood because its first anal plate is a part of the tube, and not of 

 the calyx wall. The large size of the radials will distinguish it from any of the 

 Ichthyocrinidae. 



The infrabasals in this family are about as in the Sagenocrinidae, with 

 occasional reduction in size to such a degree that they do not appear beyond 

 the column. The posterior basal throughout is elongated much beyond the size 

 of its fellows, forming the support of the more or less symmetrically placed anal 

 tube. Along with the anal tube the two earlier forms of radianal are found in 

 the pre-Devonian genera ; and its migration to a higher position, if that is what 

 occurred, or its complete elimination, is strongly illustrated in the Devonian and 

 Carboniferous genera. There is of course no room here for forms without any 

 anal plate. In the brachial system there is a very regular progressive develop- 

 ment from two primibrachs in the Ordovician and Silurian to three or more in 

 the Carboniferous. The change took place in the Devonian, where both forms 

 occurred with occasional variability within the same species. 



The Taxocrinidae were the earliest of the Flexibilia in time, beginning in 

 the Ordovician with Protaxocrinus, which stands in very close relation to cer- 

 tain Inadunate forms of that age. The family is represented in the Silurian 

 by three genera, and in the Devonian by three, two of which pass into the Car- 

 boniferous; but it is preeminently a Carboniferous type, culminating in the 

 strong genus Taxocrinus and the highly specialized Onychocrinus, both of 

 which continued with numerous species until the close of the Lower Car- 

 boniferous. 



All of the genera, with the exception of Parichthyocrinus, are common to 

 both Europe and America. 



