344 The American Geologist. December, L903 
its kind in middle Pennsylvania and is so common in the Ham- 
ilton upper shale (among its extensive marine fauna) that its 
very abundance in the absence of every other known form of 
plant, except Spirophyton (Taonurus), is sufficient to awaken 
suspicion of its vegetable nature. 
Some other imperfect specimens are referred to various 
genera and species in the works indicated above but little or 
nothing is known of them within our district. In Canada, a 
larger flora is credited to the Hamilton or Middle Devonian by 
Sir Wm. Dawson and apparently the development of the De- 
vonian flora was more advanced or more varied and abundant 
in that region. 
A similar story may be told of the overlying Genesee, Port- 
age and Catskill. Dadoxylon (clarki) continues through the 
Genesee and Sporangites abounds. The more sandy Portage 
and Chemung are crowded in many places with plant-rags and 
other obscure relics of vegetation. An Asteropteris, Lepido- 
dendron chemungense, the so-called Sigillaria vanuxemi, a 
stump of a tree-fern (Caulopteris lockwoodi), an Archseop- 
teris or two, with a Spirophyton, are almost all the distinguish- 
able forms yet described. 
Nor is the Catskill more productive, though some species 
occur there in finer condition. The quarries at Meshoppen, 
Pennsylvania, have yielded to Mr. Lacoe excellent specimens 
of Archaeopteris (Cyclopteris) hibernica, with Rhaciopteris, 
and more lately, the magnificent Dictyocordaites of Dawson. 
The little Sigillaria (Sigillaria simplicitas) with its uncouth 
specific name, may mark the beginning of that stately genus. 
IX. THE CLADODONT SHARKS OF OHIO. 
T1 f: genus Cladodus has long figured in palaeontology, in 
consequence of the great abundance of the peculiar teeth to 
which the name was originally given, and which were the only 
parts of the fish of which we had till lately any knowledge. 
Consisting of a medial cusp standing on a straight t-dgc of a 
wide, flat, semi-elliptical base, with one or more lateral den- 
ticles on each side, they formed an easily recognized and unique 
type of fossil and many species have been described both here 
and in Europe indicating beyond doubt the existence of elasmo- 
branch fishes in considerable force in the palaeozoic seas. 
