64 



A. H. Clark — Study of Recent Crinoids. 



The recent species of Holopus is : 



Holopus rangii d'Orbigny 



The frequency according to depth of the recent representa- 

 tives of these genera is as follows : 



0- 50 



4 



550- 600 



4 



50-100 



6 



600- 650 



4 



100-150 



5 



650- 700 



4 



150-200 



4 



700- 750 



3 



200-250 



3 



750- 800 



3 



250-300 



3 



800- 850 



3 



300-350 



3 



850- 900 



3 



350-400 



3 



900- 950 



3 



400-450 



3 



950-1000 



2 



450-500 



3 



1000-1100 



2 



500-550 



3 



1100-1200 



2 



1200- 



-1300 



1 





The frequency according to temperature of the recent repre- 

 sentatives of these genera is as follows : 



70°-72° 



1 



50°-52° 



1 



68 -70 



1 



48 -50 



2 



66 -68 



1 



46 -48 



1 



64 -66 



1 



44 -46 



1 



62 -64 



2 



42 -44 



1 



60 -62 



2 



40 -42 



1 



58 -60 



2 



38 -40 



2 



56 -58 



2 



36 -38 



2 



54 -56 



1 



34 -36 



1 



52 -54 



1 



32 -34 



1 



In the following table is given a comparison between these 

 genera and the genera confined to the Indo-Pacific, confined 

 to the Atlantic, and common to both oceans. 



The most noticeable fact in regard to the recent genera with 

 fossil species is their very restricted geographical distribution ; 

 aside from Democrinus none of them occur in more than one 

 ocean basin, and, moreover, they occupy collectively only a 

 very small portion of the present seas. 



They are entirely confined to two small areas, (1) in the west 

 Pacific from the Malay Archipelago to southern Japan, and (2) 

 in the west Atlantic from the West Indies to Iceland, Ireland 

 and Norway. 



This distribution is particularly interesting when compared 

 with the almost identical distribution of the Xiphosuridse 

 (Horseshoe Crabs), Lingula, and other ancient types. 



