178 NEW YORK STATE MUSEUM 
tris as 6:9 (8.5-—10); and in the different outline; the former having a 
squarish carapace with subparallel sides and straight frontal margin and 
subrectangular anterior angles, while in the latter species the sides 
are more convergent and the anterior angles more rounded. Specimens 
are, however, common which it is difficult to assign to either species, partly 
on account of their original intermediate form and partly because of 
secondary changes through lateral compression. The average represen- ’ 
tatives of E. lacustris are considerably larger than those of 
E.remipes although a few carapaces of the latter species indicate that 
it did not fall much short of the other type in size attained. Nevertheless 
the great majority of the specimens of E. remi pes obtained in the 
central New York region are very much smaller. No differences have been’ 
observed in the proportions of the abdomen and the appendages (including 
the metastoma), save perhaps the swimming legs, in which a tendency to 
greater broadening is observable in E. lacustris, and this has led to 
the variety pachychirus. : 
A variety robustus of the present species has been distinguished 
by Hall, in regard to which it is stated that: ‘“ The form of the anterior 
feet and the swimming feet are essentially the same, while the joints of 
the body are proportionately longer and stronger, furnishing sufficient 
ground for a variety, but not satisfactory evidence of specific difference.” 
In the explanation of his figures [plate 8rC] a note is added saying that 
further examination with other species has shown that the form has the 
characters of a distinct species. The difference supposed to rest in the 
greater length and strength of the abdominal segments is due to the post- 
mortem separation of the segments as far as the stretching of the connecting 
membranes permitted, while on the other hand, Hall’stypesof E. lacus- 
tris are all somewhat contracted through sliding of the segments over 
each other. We have been unable to find other differences and therefore 
consider robustus as only a preservation state. 
