IN THE DEVELOPMENT OF COMATULA. 



249 



From Stephanocrinus, the transition is not difficult to the remarkable genus 



Fig. 4. 





.•>^= 



^ 



a 



<3^ 



.^^^0. 



^^. 



P 



<% 



Plan of Stephanocrinus. 



1. Basalia, .... 3 



2. Radialia 5 



3. Inter-radialia, . . 5x2 



4. Axillary, . . . . 5x2 



Fig. 5. 



Eucalyptocrinus, in which the roof is greatly 

 elevated, and is composed of five series of inter- 

 radial plates alternating with five series of 

 axillary plates, having the arms lodged in deep 

 grooves between them (woodcut, fig. 5). If the 

 arms and axillary plates were here suppressed, 

 and each of the inter-radial series simplified by 

 reduction in the number of its constituent plates, 

 we should have the portion which surmounts 

 the calyx, and gives so singular a physiognomy 

 to this curious Crinoid, presenting essentially 

 the same composition as in our larval Comatula. 



In Eugeniacrinus, however, if we adopt the 

 very elegant synthesis of this genus as proposed 

 by QuENSTEDT,* WO must, instead of regarding 

 each of the five pieces which form the pyramidal 

 roof as an inter-radial, interpret it as an axillary piece inseparably united to the 

 last radial. The roof of Eugeniacrinus would thus have a different signification 

 from that of the roof in the larval Coma- 

 tula. 



If in Eucalyptocrinus the inter-radial 

 series were suppressed,; while the axillary 

 series, simplified by the reduction in 

 number of their constituent elements, 

 were, as the others became suppressed, 

 correspondingly developed, so as to bring 

 their lateral edges into contact ; and, 

 finally, if the arms were liberated from 

 their adhesion to the roof, — this genus 

 would, so far as the characters involved in 

 the changes here supposed are concerned, 

 be converted into a Eugeniacrinus. While, 

 on the other hand, as we have already 

 seen, the lateral development of the inter- 

 radial series, and the entire suppression 

 of not only the axillary series, but the 

 arms, would so far convert it into the larval Comatula. Eucalyptocrinus thus 



ambulacral zone, a character incoi sistent with cystidian morphology. Dujardin with more reason 

 places Stephanocrinus in his family of Haplocrinidce. The so-called ovarian pyramid of this genus 

 seems to me much more probably an anal orifice. 



* Ueber ^M^em'acnm'ies caryop%Zia<ws in Neues Yahrbuch fiir Mineralogie, &c. 1855. P. 669. 



VOL. XXIII. PART II. 3 Z 



Flan o/ Eucalyptocrinus after de Kokinck. 



1. Basalia, 5 



2. Eadialia 5x3 



3. Inter-radialia, . . . 5x5 



4. Axillary, 5x3 



