NO. 7 SEA-LILIES AND FEATHER-STARS CLARK 3 



Suborder Oligophreata. 



Family Charitometrids. 



Family Thalassometridse (including the subfamilies Ptilometrinse [fig. 



46] and Thalassometrinse). 

 Famil}' Calometridae (fig. 45). 

 Family Tropiometridse. 

 Family Colobometridje. 

 Family Mariametridae. 

 Family Stephanometridse. 

 Family Himerometridse. 

 Family Zygometridse. 

 Family Comasteridse (including the subfamilies Capillasterinse, Comac- 



tiniinse [fig. 44] and Comasterinje). 



THE INTERRELATIONSHIPS OF THE CRINOID SPECIES 

 The various crinoid species are of very different relative value. In 

 some comatulid genera, especially those including species with many 

 arms, if any one character whereby the species are commonly dif- 

 ferentiated be plotted on a species curve the several species will be 

 found to be indicated not by a series of separate triangles, but by a 

 succession of more or less marked nodes which are united to the mass 

 forming the adjacent nodes by coalesced bases in thickness equal to 

 from 10 to 60 or more per cent of the maximum height of the neigh- 

 boring nodes. Such variability and lack of absolute fixity in any one 

 character is as a rule reflected in all the characters, and thus there 

 results a species group or genus which may be compared to a small 

 mountain system rising out of a plain each peak of which represents 

 a recognized form. In such a genus every character varies between 

 two extremes, but there is often no correlation whatever between the 

 different characters. Thus every sort of combination is possible and 

 a very large variety is found, though the tendency is for the characters 

 to form more or less definitely correlated groupings and to crystallize 

 into certain definite types. 



This type of variability is not connected with the geographical 

 origin of the specimens except in a very general way ; it is chiefly seen 

 in the multibrachiate species of the Oligophreata, and in specimens 

 of these species from the East Indian region, though there are one or 

 two good examples in the Caribbean Sea. In the Indo-Pacific many 

 species which occur in numerous well-marked varieties in the Malayan 

 region when extending their range outside of this region gradually 

 become more and more fixed and definite in their characters so that 

 individuals from, for example, Madagascar or southern Japan, are all 

 found to be practically uniform in their various features and to 

 represent the mean of the two extremes seen in a series from the 

 central East Indian region. 



