VI 
INTRODUCTION. 
at all costs might prefer Belocrinus to Metablcistus, and Dimorphicrinus 
to Orophocrinus ; but in those instances the facts are open to question. 
In a few instances the change is not one of nomenclature alone, hut 
consists in assigning certain specimens to a systematic position different 
from that in which they have hitherto been placed. Such changes are 
the result of a renewed examination of the specimens themselves, with 
better aids to comparison than those at the command of previous investi¬ 
gators. In the case of species inaccessible to the compiler, the views of 
the latest recognized authorities have been followed. The List is in no 
sense a revision. 
The citations of literature are those hearing on the name or systematic 
position of the genus or species in question. They do not profess to afford 
an exhaustive guide to the literature of the Blastoidea. Nevertheless, 
reference to the authorities quoted will probably place the student in the 
way of finding out all writings on the subject that are of any importance. 
With the exception of two references to D. D. Owen’s ‘ Catalogue of 
Geological Specimens illustrating the formation of the Ohio Valley,’ 1843, 
and two to G. Troost’s 4 Geological Reports to the General Assembly of 
the State of Tennessee,’ 1840, 1841, all the citations have been verified 
afresh for this work. 
The specimens preserved in the Geological Department of the British 
Museum are catalogued under the names of the several species to which 
they are now referred. But when a specimen has previously been alluded 
to in scientific publications by one or more names, those names are here 
repeated in italic type in chronological order. Specimens that have never 
been so alluded to have no such italicised name, but are prefaced by a 
■-., which in each case stands for the name in broad-faced type 
that immediately precedes it. 
It follows from the foregoing paragraph that the italicised name is the 
sign of a historical specimen. Those specimens which have been figured 
are to be detected by the reference to the figure, which forms part of the 
bibliography of the specimen. Those specimens which have served as 
types are distinguished by the letter fC, which is always placed imme¬ 
diately after the reference to the publication in which the specimen was 
used as a type. The use of the word type and of the sign %, requires 
some explanation. The increased importance attached by modern 
systematists to these type-specimens has led to a more rigid definition of 
the term, and to a classification, with its appropriate terminology, of the 
various degrees of authenticity pertaining to those specimens which former 
writers confused under the one designation 4 type.’ The terms now 
coming into vogue have not been used in the body of this work, since it 
was felt that their brevity and convenience might not counterbalance 
their present unfamiliarity. The ideas expressed by the chief of these 
terms may, however, be recalled here in the form of definitions. 
