180 NEW YORK STATE MUSEUM 
cal lacustris, but a survey of the larger collection of specimens 
since gathered from the Bertie waterlime of Buffalo leaves no doubt 
that there are numerous examples with equally broad swimming legs 
which are not otherwise distinguishable from E. lacustris and 
that furthermore there occur transitional forms between the two in this 
regard. 
The additional characters, the stronger sculpturing. etc., are taken 
from the type specimen [op. cit. pl. 82, fig. 1] which also retains a swim- 
ming leg not shown in the figure. This specimen differs markedly in state 
of preservation from the great majority of the Buffalo specimens, in not 
being preserved in a black, perfectly attenuated film, but in bas-relief 
and with a light brown film, upon which the scales distinctly show. This 
different preservation is due to the conservation of the fossil, not in the 
mud rock of the typical waterlime, but in a lighter, dolomitic, slightly 
coarser grained, somewhat uneven bedded rock that contains Leperditia 
scalaris and Orthothetes interstriata. This forms the 
top stratum of the Bertie, at Buffalo, directly underlying the Cobleskill. 
There are two other specimens from this bed in the Museum of the Buffalo 
society of Natural Sciences and one in the State Museum, all of which 
retain the surface ornamentation in like distinctness and one of which 
possesses the broad swimming legs of pachychirus; but in all 
other characters they are indistinguishable from E. lacustris, espec- 
ially in regard to the carapace. 
We have for these reasons here placed pachychirus with 
E. lacustris asa variety distinguished by its tendency to a broad- 
ening of the swimming legs, and consider the other distinctive characters 
cited by the author of the species as due to the preservation of the material. 
It may be added that the exposure of the elevated anterior band of the 
segments and of the line of scales at its posterior margin is due to a pulling 
of the integument before entombment. 
