180 PROCEEDINGS OF THE ACADEMY OP [1881. 



separated except by means of the basal portions. There are sim- 

 ilar examples in the Silurian and Devonian, which will be noticed 

 later. 



If^ therefore, it be true that the underbasals had no important 

 bearing or influence upon the general structure of the Crinoids, 

 there is no good reason for making their presence or absence a 

 family character, and basing thereon a division to rank with the 

 Cyathocrinidic and Ichthyocrinidae, whose fundamental structural 

 plans offer broad and unmistakable distinctions. Nevertheless, 

 they are not without importance in classification, and certainly 

 characterize a group of more than generic value. We have accord- 

 ingly brought together the genera of this family in which these 

 plates exist under the name '■'' Rhodocriniclse.'''' 



The great family SphajroidocrinidiB includes a vast variety of 

 forms, and a mere separation of these into genera does not meet 

 the requirements of a systematic classification. We find that the 

 genera fall naturally into groups which are well defined. These 

 subordinate groups, which are three in number, we consider to be 

 sub-families, and have arranged them in the following manner : 



1. Platycrinid^. — Underbasals wanting ; basals and first radials 



forming the greater part of the calyx ; succeeding primary 

 radials very small or rudimentary ; all higher orders of 

 radials embraced within free rays ; interradial system but 

 little developed. 



2. AcTiNOCRiNiD^. — Underbasal wanting ; calyx composed of 



basals ; two or more ordei'^ of radials : well developed 

 interradial, and often interaxillary series. 



3. RnoDOCRiNiDiE. — Underbasals present ; calyx composed of 



basals and several orders of radials ; interradial system 

 well developed. 



Before proceeding to the more detailed consideration of these 

 groups, we will consider the difl!erent parts of which the body in 

 the Sphreroidocrinida3 is constructed, and this will throw 

 additional light upon the relations of the subdivisions. 



