60 A. H. Clark — Study of Recent Crinoids. 



Akt. V. — A Study of the Recent Crinoids which are Con- 

 generic with Fossil Species ; * by Austin H. Clakk. 



In attempting to interpret past conditions by an intensive 

 study of the present, one of the most natural methods is a 

 direct comparison between congeneric fossil and recent forms. 



Unfortunately this method is beset with difficulties, for 

 recent types with abundant fossil congeneric representation 

 are usually rare and local, or occupy very specialized and cir- 

 cumscribed habitats, while abundant and widely spread recent 

 types usually are represented by a very few rare and local close 

 fossil relatives. 



The great preponderance of the fossil over the recent stalked 

 crinoids has given rise to the idea that in this group more than 

 in others such a study might be of value ; but when we exam- 

 ine the situation in detail we see that the recent crinoids in this 

 respect are scarcely more promising than many other types of 

 marine organisms. 



In the present seas there exist 21 genera of stalked crinoids, 

 which are distributed among 6 families (Pentacrinitida, Apio- 

 crinidse, Phrynocrinidae, Bourgueticrinidae, Holopodidae and 

 Plicatocrinidse), falling in two orders (Articulata and Inadunata, 

 the latter including the PlicatocrinidaB only). Of these 21 gen- 

 era only 5 (if we consider Proisocrinus and Carpenter ocrinus 

 together as the recent equivalent of Millericrinus) possess 

 fossil species, while one of the families (Phrynocrinidae), in- 

 cluding 2 genera, is recent only. 



The recent genera of stalked crinoids, together with the 

 fossil genera in the families to which they belong, are given in 

 the followinp; list: 



Order Articulata 



Pentacrinitida 



Kecent Fossil 



ISOCRINUS IsOCUINUS 



Metacrinus Pentacrimis 



Hypalocrinus Malanocrinus 



Teliocrinus (Comastrocrinus) Austinocrinus 

 Endoxocrinus 



* Published with the permission of the Secretary of the Smithsonian 

 Institution) 



