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 swimming 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, especially in regard to the carapace.
We have for these reasons here placed pachychirus with E. lacustris as a variety distinguished by its tendency to a broadening 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.
