652 THE CEmOIDEA CAMERATA OF NORTH AMERICA. 



to pick out several score of tliem, wliose surface markings would in no two 

 be exactly alike, and which might in sufficiently energetic hands be made 

 into as many species. Among the smooth species of the Burlington group 

 there are several forms, which it is absolutely impossible to separate from 

 the shape and proportions of the dorsal cup alone. The arm structure indi- 

 cates that there is more than one species, but unless the arms are attached 

 the best Crinologist cannot identify them. Even the number of arms, upon 

 which great stress has been laid by some authors, cannot always be depended 

 upon imless associated with other characters. Specimens of the same species 

 may have four to six arms in one ray, and only two or three in an- 

 other. Exceptions to the general rule are nowhere more frequent than in 

 Plat//cnmis. 



All attempts at describing new species will be worse than useless if made 

 without at least some reference to the ontogeny of the Crinoids generally, 

 and of the particular group in hand. The modifications due to individual 

 growth in Platycrinus are particularly well known, and are very striking. 

 In the mature specimen the basal cup is proportionally deeper ; the radials 

 more elongate ; the stem joints, wiiich are circular in the young, become 

 elliptic ; the arms gradually change from uniserial to biserial, and from zig- 

 zag to nearly straight ; the arm joints are proportionally much longer in the 

 young than in the adult ; the pinnules much stouter and further apart ; and 

 the orals grow relatively smaller as they are carried inward by increas- 

 ing perisome. Unless all these matters ai'e taken into consideration, the 

 describing of species amounts to little more than description of individual 

 specimens. This in many cases is not without value in bringing to the 

 knowledge of others a really new form, but when carried to excess it is 

 the terror of the systematist who has to overhaul the work. Neverthe- 

 less, there are writers who go on describing so-called new species upon 

 the most imperfect material, from horizons from which numerous species 

 of the same genus have been previously described, without comparison 

 with the types or with authentic collections of known species. The earlier 

 authors, in the infancy of Palseontology, before the great treasures of our 

 crinoidal faunte had been broughl to light, and without knowledge of the 

 embryology of the Crinoids, may readily be excused for describing their 

 species from such material as they had. But at the present day the only 

 excuse for this class of work that can be found is the desire of the authors 

 to see their names appended to the greatest possible number of species. A 



