1084 The American Naturalist. [December, 
approaches Prasopora, and ought perhaps to go with the Monti- 
culiporidae. This disposition, however, necessitates the adoption 
of one of two courses, — either a new genus would have be estab- 
lished, or the species would have to go under Prasopora." 
Here we have an acknowledgment from one of the most in- 
dustrious makers of new genera and species, of their great indefi- 
niteness in this group, and of the difficulty of establishing limita- 
tions. It is exactly what should be expected. Believing in the 
evolution of many forms from one or a few primitive ones, we 
should be prepared to find in early geologic times genera and 
species beginning to differentiate. The Monticuliporoido first ap- 
pear, as far as now known, in the chazy rocks of Canada, two 
species having been described in 1859, while a third has been 
lately recorded. In the Trenton period there is a sudden increase 
in the number of species, forty-four having received distinct 
names, while in the next period, that in which the Cincinnati rocks 
were deposited, no less than one hundred and eighteen names 
have been given to the different forms. It is not at all improbable 
that many of these are synonyms, but there can be no doubt about 
there being a great increase in the number of species during Cin- 
cinnati time. So, — too, there were introd!iced two new types of 
growth the massive and the frondescent, while there was at the 
same time a great increase in the the parasitic forms. In the 
Niagara period came a reduction in the number of species of true 
Monticulipora, and definite differentiation into genera began. The 
forms are nearly all ramose; the parasitic forms seem to have dis- 
appeared and true polyzoa, like Paleschara, to have taken their 
place. The Fistulipora-like forms assume predominance, and 
Monticulipora proper dies out. This is seen in the great increase 
of species referred to Callopora and Trematopora, both synonyms 
or very close allies of Fistulipora. This genus again is related to 
Ch.nctetes, which in its turn is allied to the Favositidai ; while this 
family, represented by twg species in the Lower Silurian, becomes 
wonderfully abundant in the Upper Silurian age. 
In another group of corals, the Cyathophyllidc-e, but three genera 
are found in rocks of Lower Silurian age, each containing only 
a few species. But in the rocks of a later age, notably the Niagara, 
