30 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



Frequency at different depths 



Frequency at different temperatures 





Average depth 775 fathoms 568 fathoms 



Average temperature 50.0 Fahr. 5-2.5° Fahr. 



IV. ARMS 



i. Arms composed of a linear series of ossicles, without IBr series. 



Bathymetric Thermal 



range range 



Pentacrinitidas ( Pentametrocrinidae 



and part of Atelecrinidae) 103-1800 33.5-60.6 



Plicatocrinidae (except Calamocri- 



nus) 266-2375 31. 1-43.9 



2. Arms dividing one or more times, or, if undivided, with IBr 



series. 



Bathymetric 



range 



Pentacrinitida? (except Pentametro- 

 crinida; and part of Atelecrini- 

 dae) 0-2900 



Apiocrinidas 505-040 



Phrynocrinidae 508-703 



Bourgueticrinida? 62-2690 



Holopodidas 5-120 



Plicatocrinidae (Calamocriiius) . . . .392-782 



Thermal 

 range 



28.7-80.O 



36.7-38.1 



38.I-4O.O 



29.I-70.75 



71.0 



38.5-43-9 



Whatever may have been the ultimate origin of the crinoid arm as 

 a structure, the immediate ancestor of the recent types certainly pos- 

 sessed arms composed of an undifferentiated linear series of ossicles. 



