392 The Galceocrinidce, 



ation or suppression in part, — due to the extreme specialization 

 of certain parts and functions at the expense of others, — ^the 

 more complex forms will be considered first, because this method 

 represents their natural sequence, and also furnishes an easy in- 

 troduction to a proper understanding of the component parts of 

 the more specialized forms, and to the nomenclature of the 

 same. 



This arrangement will place Calceocrinus last, as it is the most 

 specialized form with which we are acquainted, and is conse^ 

 quently furthest removed from the as yet undiscovered or un- 

 recognized five-armed ancestor. 



I have revised the family, because the revision of Wachsmuth 

 and Springer, — while a departure in the right direction, — is not 

 quite satisfactory, for the reason that the consolidated base as 

 defined by them agrees only with the base of Calceocrinus, and 

 the true relations of the plates of the posterior side are not 

 recognized. The arm-structure also varies more than that re- 

 vision would indicate. 



CASTOCRIWUS n. gen. 



Calyx hanging against the column, and generally having a slight 

 groove for the reception of it. Column straight or nearly so. Arma 

 four, one anterior, two lateral, and one posterior, the latter being to 

 one side of the median line, — the anal plate and ventral tube occupying 

 the opposite side. Anterior arm simple (?) or bifurcating; bifurcations 

 bearing pinnules. 



Lateral arms bifurcating once, with lateral armlets given off on 

 alternate sides at every second joint beyond the place of bifurcation. 



Consolidated base with the columnar facet on the posterior portion of 

 the incurved margin. It is composed of two lateral basals, which meet 

 posterior to the column, but are separated anterior to it by the attenu- 

 ated apices of the anterior basals, or their anchylosed equivalent. 



The anterior basals occupy the median pdrtion of the anterior margin 

 of the piece, the lateral basals occupying the outer portions. 



Anterior radial higher than wide, usually narrow, and supporting the 

 anterior brachial. Lateral radials irregularly hexagonal. Posterior 

 radials irregularly triangular. Azygous elongate and placed between 

 the two posterior brachials, which extend downwards between it and 

 the posterior radials. 



Anterior arm simple (?) or with four or more brachials, upon the last 

 of which a bifurcation takes place. Bifurcations pinnulate; pinnules 

 long; lateral arms having two brachials, the second of which is axil- 



