406 The Cakeocrinidce. 



FrocUvocrinus and Calceocrinus might more properly be so- 

 termed, except for the reason that in them it is the result of an 

 anchylosis and modification of the azygous of the primitive 

 forms with the first anal. 



In Proclivocrinios the cross-bar of the T represents the first 

 anal, and the stem the remains of the azygous; while in Calceo- 

 crinus the modification has gone still further, and the stem has 

 become absorbed entirely — only the cross-bar remaining. 



The modifications undergone by the members of this family 

 will afford an interesting chapter in evolution, if the material 

 ever presents itself which will allow of its complete working-out. 



That the ancestral form was five-armed, there can seem to be 

 no doubt, as the existence of the right brachial in the four- 

 armed Castocriniis points conclusively to such a one. But 

 whether this, as yet unknown or unrecognized, ancestor under- 

 went the loss of its fifth arm after the crinoid had assumed the 

 pendulous position of its calyx, and consequently formed a 

 member of the Oalceocrinidse, or sustained this loss first and 

 consequently belonged to another or a new family, — only the 

 finding of it can set at rest. 



That Catillocrinus, — the affinity of which to the Calceocrinidae- 

 Wachsmuth and Springer have pointed out, — does not belong in 

 the line of their evolution, is shown both by its structure and 

 its geological position ; although it may and probably did orig- 

 inate from the same stock. 



The course of their specialization and modification of func- 

 tion among the known genera is shown in the successive steps 

 from Castocriniis through ProclivocrinuSy or some allied undis- 

 covered form, to Calceocrinus. 



But a more complete discussion of the reasons for the sup- 

 pression of the posterior arms, on account of their being in the 

 way in its new position, and the consequent lateral contraction 

 of the calyx with its concomitant shortening, and the progres- 

 sive development of the anterior arm and side to make up for 

 the aborted posterior side, — I will leave for another paper at 

 such time as the opportunity for the examination of a more com- 

 plete series of forms shall present itself. 



The types of Proclivocrinus radiculus, Calceocrinus halli, C. 

 iypus, and C, contractus, are in my collection. 



