288 HENRY SHALER WILLIAMS 
and under the name Pleurodictyum problematicum Goldf. is a char- 
acteristic Devonian form of Europe as well as America. 
Since all other genera in the list are known to have been 
present in the western Devonian fauna, there appears no posi- 
tive evidence of a generic character to point to any double 
origin of the fauna. 
Mr. Weller also cites a number of species as evidence of 
origin from two sources. Those traced to species in the western 
Devonian fauna require no comment; those for which an eastern 
origin is suggested are the following: Athyris hannibalensis Swal- 
low, (A. spiriferoides) ; Leptena rhomboidalis; Orthis Michelini (O. 
vanuxeml).: LEeccylomphalus paradoxus (E. laxus); Loxonema cf. 
hamiltone. 
Regarding the origin of these species, it may be said in gen- 
eral that the presence of closely allied forms in one Devonian 
fauna and nothing at all like them in a second great province, 
might be regarded as pointing to an origin from the first rather 
than the second source, but if there are species with equally 
close affinity in both provinces, then some other evidence must 
appear before we can say from which the later fauna has arisen. 
Athyris hannibalensts may have found its ancestors among the 
common and very variable A. concentrica von Buch, of the 
European Devonian, as well as from the more specialized A. 
spiriferoides of the New York Hamilton. 
Leptena rhomboidalis is such a widespread, old and variable 
form that it would not be safe to say that it was wanting in any 
complete Devonian fauna. 
Orthis michelint may have arisen from the O. vanuxemi of the 
Iowa Hamilton as well as from the same species in the eastern 
fauna. 
Any species of genera of such wide range and variable char- 
acter as either Eccyliomphalus or Loxonema cannot be safely cited 
as evidence without particular study and the discovery of some 
special distinguishing mark. 
Eccyliomphalus Portlock is cited as a synonym under Phanero- 
tinus Sow. by Zittel as having a range from Silurian to the Car 
