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NOTES ON THE PLEUROTOMIDAE WITH DESCRIP- 
TION OF SOME NEW GENERA AND SPECIES. 
Taos: i}, CasEy. 
_ In the *‘ Structural and Systematic Conchology ’’ of Tryon, 
the family Pleurotomidae is restricted to two genera — Pleu- 
rotoma and Halia. The latter of these being somewhat doubt- 
ful in its relationship, we may assume that in the original 
opinion of Tryon the family Pleurotomidae is made up of the 
single genus Plewrotoma, which he separated into a number of 
named groups relegated to subgeneric rank. Now while per- 
fectly true that, with our present lights, well-nigh insuperable 
difficulties beset us in striving to define isolated aggregates of 
species and classify them in a satisfactory manner, it none 
the less appears to the writer that the course suggested by 
Tryon was unphilosophic. Although there seems to be 
scarcely any limit tothe number of genera that might be pro- 
visionally admitted—a recent study of rather more than 
600 species living and fossil, most of which are in my 
cabinet, apparently indicating nearly or quite 250 genera, 
based principally upon embryonal structure, form and 
position of the anal sinus, form and extent of the 
canal and general type of sculpture —that is no adequate 
reason for holding all this diversification of structure and 
evidence of adaptation to greatly varied environments among 
at least 3000 species, from the Cretaceous to the present 
time, to be comprised within a single genus. Later, in the 
‘¢Manual of Conchology,’’ Tryon considerably modified 
his original views and admitted several distinct genera 
which he assigned to sundry groups held to have subfamily 
rank, but, in this case, it would appear that he rather over- 
estimated the taxonomic importance of certain genera. 
Granting that the family under consideration comprises 
only the two genera Plewrotoma and Halia, as originally 
(123) 
