212 ECHINODERMATA. 



and others do not. It is therefore of the first importance to ascertain whether^the 

 crinoid has one or two circles of plates below the radials. Those having only one 

 circle have been called monocyclic, and those having two circles dicyclic. The circle 

 at the base is composed of what we call the " basal plates," and the second circle, 

 whenever it has an existence, is composed of " subradial plates." In this we follow 

 Billings, Meek, Agassiz, and most other standard authors. Carpenter and Wachs- 

 muth call the "subradials" the "basals" in all cases where they occur, and the 

 lower plates "underbasals ;" but where there are no "subradials," they follow the 

 well-established nomenclature in calling the first circle of plates " basals." 



The presence or absence of regular interradials, it seems, should always be re- 

 garded as of family importance. 



The number of basal plates should also be regarded as of family importance. 

 If not in all cases, then in connection with the general structure of the calyx and 

 vault the families will be sufficiently well-defined. Those characters upon which 

 genera are founded, when combined, in certain associations will form families ; and 

 under this head several important families have been created. 



Generic characters, as a matter of course, are to a certain extent included in 

 the family characters ; but the form and construction of the column is of generic 

 importance. The general form of the calyx and vault, and the number of primary 

 radials, and the construction of the azygous area, are always of generic importance. 

 Beside, certain combinations and associations of what are usually regarded as 

 specific characters have been made the basis for establishing genera. 



Wachsmuth, speaking from experience, says in young crinoids the basals are 

 the most perfectly developed parts; they attain nearly their full size in young in- 

 dividuals, greater in proportion than the subradials and radials, which are com- 

 paratively early developed, and at a time when the interradial and anal plates have 

 scarcely made their appearance. The latter develop the slowest, and in some 

 genera increase continually, both in size and number, during the growth of the 

 individual. Abnormal growths, or sudden modifications of specific characters, 

 almost always take place in the interradial and azygous areas, the azygous rays and 

 dome. His experience is corroborated by others, and the author never saw a small 

 specimen that did not have its basals or first circle of plates as distinctly marked as 

 they occur in large specimens of the same species. 



The columns of crinoids very frequently show injuries received by the animal 

 in its life-time. The column is sometimes much swollen on one side and depressed 

 on the other; sometimes a parasite that attached to the column is found imbedded 

 or enveloped in the crinoid column. The animal could also repair its arms and 

 other parts of its body by secretions of lime in the same way. 



Some of the Cystoidea may be arranged into families, upon characters similar 

 to those upon which families are founded in the Palaeocrinoidea ; but, generally, 

 this is not the case. Some of the Cystoidea possessed an arabulacral opening and 

 two other orifices, the purposes of which may not be fully understood ; in others, 

 the two openings referred to are absent. In addition to these, many bear openings 

 called "pectinated rhombs," and all have pores passing through the plates. These 

 pores passed to organs called ' ' hydrospires," which were largely developed within 

 the calyx of the Cystoidea and Blastoidea. The communication, through the test, 

 with the outside water is supposed to show the hydrospires belonged to the respira- 



