134 CLARK: BATHYMETRICAL DISTRIBUTION OF CRINOIDS 



to the association of genera in the older horizons, suggests 

 that the older types not only possessed a very limited range 

 of possible creative evolution and development, but that, in 

 contrast to the later types, the new forms which they gave off 

 were not adapted to meet special conditions, but rather to exist 

 side by side with the parent types, utilizing the excess of avail- 

 able food. As would be expected, a small number of the groups 

 of the present day (for instance the Comasteridse) appear to be 

 giving off, or attempting to give off, new types in this way. 



The series of figures showing the average range expressed 

 as a percentage of the average depth suggest that in the older 

 and less specialized groups the tendency is for the average range 

 to equal or to exceed the average depth of habitat, but in the 

 more recent and more specialized types to be less. The figures 

 (which are given in the following tables) are, however, not 

 conclusive. 



per cent per cent 



Comasterinse 50 ColobometridsB 71 



Comactiniinse 50 Calometridae 72 



Antedoninae 52 Bathymetrinse 75 



Mariametridse 58 Bourgueticrinidae 80 



Heliometrinae 60 Capillasterinse 81 



Thysanometrinae 64 Zenometrinse 82 



Himerometridse 66 Perometringe 85 



Zygometridse 66 Charitometridse 91 



Pentacrinitida 67 Ptilometrinse 98 



Thalassometrinse 67 Plicatocrinidae 145 



Pentametrocrinidae 69 Atelecrinidae 244 



Average 68 per cent. 



Contrasting the more specialized with the less specialized 

 types: 



per cent per cent 



Articulata 144 Inadunata 145 



Pentacrinitidse 77 Bourgueticrinidae 80 



Comatulida 90 Pentacrinitida 67 



Oliophreata 70 Macrophreata 96 



Average 95 Average 97 



Considering the groups including stalked forms: 



per cpnt 



Pentacrinitidse 77 



Pentacrinitida 67 



Bourgueticrinidae 80 



Plicatocrinidae 145 



