INTRODUCTION. 
Vll 
Holotype .—The single specimen selected as the standard of a species or 
variety, either by the fact of its being unique, or by the definite 
statement of the original author, or, in default of such statement, by 
the first subsequent author who may have restricted the species. If 
but a single specimen was figured by the author of the species, that 
specimen, unless confessedly abnormal, is regarded as the holotype. 
Cotype .—When a species was based upon more than one specimen, and 
when none of them was selected as holotype, then all the original 
specimens rank as cotypes. 
Pciratype .—When a species was based upon more than one specimen, and 
when one has been selected as holotype, then all other original 
specimens are called paratypes. 
Metatype .—A specimen that did not serve for the original description of 
the species, but that came from the same locality (and, in the case 
of fossils, from the same horizon), and that has been definitely 
determined as representative of his species by the original author. 
As for the sign ^ in the following List, it is affixed to all holotypes and 
cotypes, whether of valid species or of synonyms. In some instances it 
is affixed to paratypes, but only when neither the holotype nor a cotype of 
the species in question is preserved in the National Collection. In no 
case is the sign ^ applied to a metatype, although, owing to the loss of 
all other type-specimens, such metatype may be the most valuable 
evidence extant for the interpretation of the original description. 
It might be thought that the publication of the present list was hardly 
necessary, seeing that only thirteen years have elapsed since the Trustees 
of the British Museum issued the classical work by Robert Etheridge, fil., 
and P. Herbert Carpenter, entitled ‘ Catalogue of the Blastoidea in the 
Geological Department of the British Museum (Nat. Hist.), with an 
account of the Morphology and Systematic Position of the Group, and a 
Revision of the Genera and Species.’ (4to. London, 1886.) There are, 
however, two reasons why such an opinion would be incorrect. First, 
as stated in the Editorial Preface to the fine volume in question, the 
authors originally intended their work as “ a Memoir on the Blastoidea 
to be presented to one of the learned Societies.” It was turned into 
a British Museum Catalogue as an afterthought, and, perhaps for that 
reason, never attained that precision in the exposition of the actual 
material in the National Collection which is nowadays considered to be 
necessary in a Catalogue. Although the Catalogue of the Blastoidea 
gives a list of those species of the class that were contained in the Museum 
in 1886, yet it is only from the plates that the reader can gain any idea 
as to the specimens in the Collection. The second reason is that, partly 
owing to the interest aroused by the Catalogue of the Blastoidea, the 
Trustees have, during the last decade, acquired, either through donation or 
