CLARK: BATHYMETRICAL DISTRIBUTION OF CRINOIDS 129 



per cent per cent 



Capillasterinse 23 Atelecrinidae •. . 50 



Zenometrinae 24 Mariametridse 53 



Thalassometrinse 29 Himerometridse 54 



Colobometridse 32 Bourgueticrinidse 54 



Charitometridae 39 Antedoninae 58 



Heliometrinse 39 Thysanometrinae 61 



Ptilometrinae 40 Comactiniinae 62 



Plicatocrinidse 41 Perometrinae 63 



Calometridae 42 Comasterinae 64 



Pentacrinitida 47 Bathymetrinae 64 



Zygometridae 49 Pentametrocrinidae 71 



Average for all families 48 per cent. 



From this list it is evident that there is no definite corre- 

 spondence between the relation of the average to the total range 

 and the systematic scheme, for closely related families, such as 

 the Capillasterinse and the Comasterinae in the Oligophreata, and 

 the Batkymetrinse and the Zenometrinae in the Macrophreata, 

 occur at opposite extremes. 



But it is interesting to observe that it is within the interval 

 41 per cent to 54 per cent, a range of only 27 per cent, or a little 

 more than one-fourth, of the total range, that the families Pli- 

 catocrinidae, Calometridae, Pentacrinitida, Zygometridae, Atele- 

 crinidae, Mariametridae, Himerometridae and Bourgueticrinidae 

 fall, these eight families, the average range of which is 48 per 

 cent, or exactly that of all of the crinoid families together, includ- 

 ing not only all of the stalked types, but also the Zygometridae, 

 the only comatulid family satisfactorily represented as a fossil, 

 and the Atelecrinidae, the only comatulid family in which the 

 primitive basals persist in the adult. In other words, we find 

 here all of the families of which we possess any definite palaeonto- 

 logical history. 



This would suggest that in ancient types still persisting the 

 normal condition is for the average range of all the genera in 

 any given family to be about one-half the total range of the 

 same family, while in the later types there is a departure toward 

 both extremes. 



Within the first half of the list there are 7 oligophreate, 2 

 macrophreate and 2 stalked groups; within the second half 4 

 oUgophreate, '6 macrophreate and 1 stalked groups. 



