444 : THE PALEONTOLOGY OF MINNNSOTA. 
[Orthis (Dalmanella) testudinaria 
collectors have almost lost sight of the original species. Some of these varieties 
seem to mark given horizons over limited areas, and others apparently characterize 
special localities; still, I do not believe they are sufficiently distinct or persistent 
enough to rank as species or to be worthy a varietal name beyond the purpose of 
the locality where found, or for local preservation.’”’ (Whitfield, loc. cit.) Specimens 
of O. testudinaria from the Trenton shales and from the lower portion of the Galena 
formation of Minnesota are slightly smaller and narrower than those from the 
Trenton of New York, while in central Kentucky they are generally twice the size 
of the eastern examples. Other specimens from the latter region are very thin-shelled 
and are referred by local collectors to O. emacerata Hall. In the Cincinnati group of 
the Ohio valley, O. testudinaria is abundant in certain horizons. It is, moreover, 
nearly always present in one form or another throughout the formation and is more 
or less variable, although constant in its characters in certain beds. Some varieties 
are known as 0. cyclus James, O. multisecta (James) Meek, O. emacerata Hall, O. jugosa 
James and O. meeki Miller. The first two are synonymous and cannot be regarded as 
of greater significance than a local variation; the same is also true of the last two. 
O. emacerata can be distinguished from O. testudinaria by its thin, compressed valves 
and finer and more numerous striw. If, however, a close examination is made 
between specimens of 0. testudinaria from various localities it will be apparent to 
the observer that individuals from one region do not exactly agree with those from 
another. As long as one restricts himself in his studies of this species to a single 
horizon of one locality all goes well with the selected varieties, but as soon as the 
trial is made to apply them to specimens from other regions the chosen varieties 
drop out for want of constancy of characters. 
In some Minnesota specimens there is a tendency to greater convexity of the 
dorsal valve. The mesial sinus may be obsolete or, as seen in one specimen, 
narrow and deep, sharply indenting the anterior margin. Probably if the develop- 
ment of the sinus were to become deeper and deeper in successive generations, it 
would eventually result in a species related to Bilobites. The general expression of 
0. testudinaria and species of Bilobites, excluding the strongly lobate condition of the 
latter genus, is essentially the same. While this may be the line of development, 
still Bilobites may have originated from an entirely different stock. Dr. Beecher, in 
his “Development of Bilobites,” has suggested its relations to the group represented 
by Platystrophia biforata Schlotheim.* 
Formation and locality.—Not common in the Trenton shales at Minneapolis, St. Paul, Cannon 
Falls, Chatfield, Preston and elsewhere in Minnesota; Decorah and McGregor, Iowa. Very common in 
the Galena shales at various localities in Goodhue and Olmsted counties, Minnesota. Also from the base 
of the “ Upper Buff beds” of the Trenton at Mineral Point, Wisconsin, and Rockton, Illinois. From the 
Galena at Decorah and Dubuque, Iowa; Neenah and Oshkosh, Wisconsin. In the Trenton Jimestone of 
*American Jour. Sci., vol. xlli, p. 54, 1891. 
