310 GEORGE H. GIRTY 
Anthracomva, and Anthrocosia in a valuable monograph published a 
few years ago. Later, after studying specimens of Nazadites from 
Nova Scotia, he reached the conclusion that Anthracoptera and 
Naiadites were the same genus. 
Thus far the balance of evidence and opinion seems to be in favor 
of the fresh-water habitat of the fauna. On the other hand, externally 
and internally, Naiadites is extremely like the marine genus M yalina, 
and Dr. Hind has referred many of our marine Myalinas to Natadites. 
In fact, he has even placed the names of some of our American 
Myalinas which always occur associated with marine faunas in the 
synonymy of English species of Nazadites which are supposed to be 
strictly fresh water. Furthermore, the fauna under consideration 
is in some instances associated with specimens of Lingula and Avicult- 
pecten. The living Lingulas sometimes inhabit brackish waters 
near the mouths of rivers, but never the fresh waters of lakes and 
streams, while the living Pectinoids are strictly marine. The fossil 
Pectinoids in question are small and depauperate examples and belong 
to a rather peculiar group, that of Aviculipecten whitet. 
This assemblage can hardly be explained as due to the accidental 
commingling of types having different habitats. If it consisted of 
fresh-water animals washed out to sea we would expect to find the 
fresh-water types few and the marine ones numerous, varied, and 
characteristic. Such is not, however, the case. One would not a 
priori much expect to find marine animals washed into a fresh-water 
fauna, and in such an event we would probably look for an entire 
marine fauna, or, at least, granting that only a few specimens were 
washed in, that some such invaders would be of the usual marine 
types. Instead, the alien forms are always limited to one or two 
peculiar varieties. That abundant and differentiated marine life 
was always at hand waiting for an opportunity to migrate wherever 
the conditions became possible seems to be evidenced by the occurrence 
now and again of marine faunas in close association with beds of 
coal. On the whole, it seems most reasonable to regard this fauna 
as a natural assemblage of species selected and modified by a habitat, if 
not in strictly marine, at least not in strictly fresh waters. 
There is another reputed occurrence of fresh-water forms in the 
Carboniferous, reported by Mr. Walcott from the Eureka district, of 
