652 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
to pick out several score of them, whose 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 unless 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 
_ Platycrinus. 
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, which 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 are 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 Paleontology, before the great treasures of our 
crinoidal faunze had been brought 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 
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