Fossils fror/i the Lower Coal Measures — Keyes. 27 
of them even minute, their great numbers made up, in great 
part at least, for the conspicuity of larger but fewer forms. 
Though the majority of the forms of this group are small it is 
not a depauperation as among the brachiopoda, as is shown by 
the individual size of each species being normal and in some 
instances even considerably above. Some of these species are 
also of interest because of their recognition for the first time 
within the limits of Iowa and hence to a considerable extent 
their previously known geographical range is increased. Other 
of the species enumerated are already known to have a wide 
geographical distribution which is suggestive of a somewhat 
extended vertical range. Among recent mollusca and especially 
land forms, a wide geographical distribution, as has been referred 
to by Binney, appears to be indicative of a high antiquit}^ for 
the group, and the corroborative evidence is abundant. A 
notable instance is the living Zonites^ four or more species of 
which are circumpolar in their distribution, and this genus, even 
a subgenus ( Co)tuIns)to which belongs one of these living forms 
ranges back to the Carboniferous; while the modern ^cnws, Pupa 
is represented in the Carboniferous by four species. Cephalo- 
pods are not abundant in the shales under consideration, and 
are represented by only two genera and five species : yet one of 
the species of Nautilus attained a diameter of 18 cm. or 20 cm. 
and an Orthoceras reached a length of 50 cm. with a diameter 
at the larger end of 5 cm. Of the lamellibranchs the majority 
are small species; but two are comparatively large, attaining a 
length of nearly 10 cm. and having exti'emely thin shells. One 
specimen is of special significance as exhibiting in all the details 
the internal features of the shell, the characteristic, well defined 
muscular scars, and the edentulous hinge margin; in fact so 
closely does it resemble in these characters, and general form 
and external appearance, a modern Anodoiita that it is difficult 
to see how it can be generically separated from it; and should 
further investigation prove that the specimens under considera- 
tion really belong to that genus it would be of unusual interest. 
The modern Unio^ Anodonta and allied genera certainly have 
a wide geographical and geological distribution, as is shown by 
the rich discoveries of Unionidte in the mesozoic and later strata 
of the west. The genus Aiiodo?ita is, if the opinion of Hall is 
