106 The American Geoloyist. February, is97 
the Maquoketa (Hudson) and Cincinnati (Hudson) series. 
Likewise 0. corpulenta Sardeson is found in botli tlie Trenton 
and the Maquoketa. Ortliis rtxjata Sardeson. is the probable 
representative of 0. rtntUisecfa Meek, and allied forms. The 
transitions have not been traced from one species to another, 
however, in any case, although one tinds O. rogafa, 0. mnlti- 
secta and 0. corpulenta very similar to each other. 
I do not find the anticipated evidence of evolutionary devel- 
opment from one species to another, except in the way of 
morphologic likeness. The geologic evidence serves more to 
prevent than to aid in forming a phylogenetic connection be- 
tween the species, since, when we have arranged the supposed 
phylogenetic lines, the geologic evidence proves, nevertheless, 
that our specimens represent contemporaneous species, not 
successive ones. Either each species has migrated to the re- 
gion where the shells are found, having been evolved in some 
other place or places in the Ordovician or in the Cambrian sea ; 
or, the change in form between one species and another has 
taken place in a few individuals, under special conditions, and 
is therefore obscure. Again, when we try to call them local 
varieties, of one species, we are compelled, by the evidence, to 
acknowledge that the "mere varieties" are distributed A-ery 
wudely, and are not local ; that, too, they existed apart and 
together under very like, as well as quite unlike condi- 
tions. In short, it is not proved by specimens in my collec- 
tion that the above described Or^^.i>, whether called species or 
varieties, are not distinct. I have, therefore, made a more 
minute morphological analysis and comparison than brachio- 
podists usually do. If the evolutionary development in Brach- 
iopoda is to be traced, it will be necessary to make clearly 
distinctions in form as minute, and even much minuter, than 
these. 
None of the above described species are like, or similar to, 
Dalman's* figures, and to the best of my knowledge, there is 
ample room for preference of Meek's viewj- that our forms 
may none of them be identical with those described as Orthis- 
iestadinaria by Dalman, or those identified with that species 
in England. The necessary material for a comparison of 
*See Pal. N. York, vol. vni, pt. 2, tab. ii, fig 4 a-c. 
tPal. Ohio, vol. i, p. 111. 
