Echinoid Radioles. 137 
radioles, whether from St. Cassian or Bakony. Here also are to be seen flattened 
spinules and collar-like expansions similar to, if not so pronounced as, those which, 
according to DorDERLEIN, are found only in recent species. In extreme cases it is 
difficult, perhaps impossible, to distinguish between the apical radioles of allied 
species, while, on the other hand, the difference between an actinal and an apical 
radiole is so great that, in the case of isolated fossils, prolonged study of a large 
series of specimens is needed before one can recognise that they belong to the 
same species. 
Another kind of variation is due to age. The peculiarities of the classes of 
radioles just described are far less marked in youth, and the radioles of allied 
species are then not so distinct. Transverse sections sometimes enable one to trace 
in a single radiole the gradual assumption of the adult features. 
The Triassic echinoids doubtless displayed those differences between individuals 
with which zoologists are familiar in their living descendants. The limits of such 
variation within a given species can only be determined by a large series of measure- 
ments of radioles similar in position on the test and in age. Such evidence is not 
afforded by the material at our disposal, and in any estimate the chances of error 
are numerous. 
Finally, in a comparison of radioles from various localities, it is necessary to 
enquire if they present such consistent differences as might be due to a change of 
environment acting on the whole assemblage at any one place. Here it is hard to 
distinguish the respective influences of place and time: contemporaneous faunas 
may exist under very different conditions, and may diverge into local races or 
species ; or similar difference may be produced in the same area by the change 
of conditions, resulting in mutations or fresh species. Whether the variant forms 
represent races or mutations must be decided upon further evidence of a nature 
familiar to geologists. Whether any particular variant is to be regarded as an 
independent species, or merely as a local race or a mutation, is a question that 
can only be answered in an arbitrary manner according to the personal opinions 
of the describer, at least until zoologists are more agreed as to the amount of 
divergence that should constitute a specific distinction. There is however a simpler 
question, namely: Should these variants receive independent names? For the same 
reasons as have already been expressed concerning crinoid columnals, I advocate 
the giving of distinct names in all cases where a distinct and constant difference 
can be detected and formulated. The describer may think himself able to distinguish 
individuals from different localities, and may have the firmest conviction that those 
individuals represent distinct species or subspecies; but until he is able to formulate 
the differences in such a way that his colleagues can share or, at least, understand 
his conviction, he has not acquired the right to burden them with a new name. 
Consider, for instance, the radioles from St. Cassian, from the Seiser Alp, and from 
Bakony. In some cases one can say that the same species appears in all three 
localities; but in other cases, though there is a resemblance, yet there are also 
constant differences, which may be minute but which can be expressed in words. 
Anaulocidaris testudo, for example, might be referred by many systematists to 
A. Buchi; but differences, capable of description and measurement, have induced 
me to denote the former by an independent name. Here, however, an objection 
may be raised. Let it be assumed, for the sake of argument, that a few specimens 
