2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J2 



The discoveries of the last few years have shown that the Hving 

 crinoids, far from being rare or few in numbers, are abundant both 

 as individuals and as species, and that in all localities where the some- 

 what exacting conditions under which they can exist are met they 

 occur, sometimes in enormous numbers. The requirements necessary 

 for the maintenance of crinoidal life are unfortunately of such a 

 nature that, though quite generally distributed in the deeper waters 

 of the oceans, they become rare or very local in the littoral, which, 

 together with the great difficulty of preserving them in anything 

 approaching satisfactory form, has served to keep them enshrouded 

 in mystery while animals of other types engaged the attention of 

 investigators. 



NUMBER AND SYSTEMATIC ARRANGEMENT OF THE RECENT 



CRINOIDS 



There are known from the seas of the present day 576 described 

 species of crinoids which are distributed in 142 genera and 28 families 

 and subfamilies ; of these, 76 species, included in 22 genera and 6 

 families, are stalked, while 500 species, included in 120 genera and 

 22 families and subfamilies, belong to the unstalked or comatulid type. 



The systematic arrangement of the families and higher groups is 

 as follows : 



Order Inadunata. 



Family Plicatocrinidae {Calmnocrinus, Ptilocrinns [fig. 42], Thalassocriniis, 

 Gephyrocrinus and Hyocrinus). 

 Order Articulata. 



Family Bourgueticrinidae (Rhiaocrinus, Bythocrinus, Democrinus, Bathy- 



crinus, Ilycrinus and Monachocrinus [fig. 39]). 

 Family Phrynocrinidse {Phrynocrinus and Naumachocrinus) . 

 Family Apiocrinidas (Proisocrinus [fig. 40] and Carpenterocrimis) . 

 Family Pentacrinidse. 



Section I : Pentacrinites (Metacrinus, Isocriiins, Endoxocrinns, 



Comastrocrinus [fig. 41] and Hypalocrinus). 

 Section II: Comatulids (see below). 

 Family Holopodidse (Holopus). 



The comatulid section of the family Pentacrinidse in the recent 

 seas has become so numerous, so widely spread and so diversified 

 that it alone has acquired all the characteristics of an order. It is thus 

 subdivided : 



Suborder Macrophreata. 

 Family Atelecrinidae. 



Family Pentametrocrinidas (figs. 49, So). 

 Family Antedonidae (including the subfamilies Antedoninje [figs. 47, 48], 



Thysanometrinse, Perometrinc-e, Heliometrinse, Zenometrinae, Insome- 



trince and Bathymetrinas). 



