successive formations. It should also be added that what 
follows relates only to the North American area, and that some 
of the types which here appear for the first time in certain de- 
posits, have elsewhere existed at an earlier period. It should 
further be said that all palaeontologists would not recognize the 
validity of some of the generic or sub-generic forms here 
enumerated, whilst others of doubtful value have been omitted 
altogether. 
In the Clinton and Niagara formations, which in this con- 
nection may be considered together, we find representatives of 
the following genera : — Lingula, Pholidops, Discina, Orthis, 
Ortliisina, Nucleospira, Leptaena, Stropliomena, Strepto- 
rhynchus, Chonetes, Spirifera, Atrypa, Athyris, Cyrtina, Rhyn- 
chonella, Pentamerus, Stricklandinia, Lcptocoelia, Camerella, 
Zygospira, and Trematospira. Most of these are more or less 
largely represented in the Lower Silurian rocks ; but Chonetes, 
Spirifera, Cyrtina, Pentamerus, Stricklandinia, Lcptocoelia, 
Trematospira, and Pholidops represent types which appear 
now to have first made their appearance in this area. In Ohio, 
the genus Trimerella also makes its first appearance at this 
period. In the Lower Ilelderberg epoch, though Brachiopods 
are very abundant, and many new specific forms come into 
existence, it is chiefly the already existing genera that arc 
represented, and the only new types that appear are Eatonia 
and Rensselaeria. In the Devonian rocks, on the other hand, 
not only are many of the older types lai’gely represented, but 
we have a large number of new types coming into existence, 
and many of these have a very striking development during the 
period. To say nothing of older types, like Chonetes, which 
are now for the first time plentifully represented, the following 
new types now make their appearance : — Ambocoelia, Amphi- 
genia, Camaroplioria (?), Centronella, Crania, Cryptonella, 
Spirigera, Leiorhynchus, Tropidoleptus, Vitulina, Terebratula, 
Pentamerella, and Productella. Of these Terebratula and 
Productella are of especial importance as being the forerunners 
of two very important groups of the class. 
We see from the above that though the Upper Silurian and 
Devonian rocks of North America were laid down as an ap- 
proximately continuous series, and certainly on an ocean-floor 
which was not once laid dry during their accumulation ; never- 
theless, new forms of life were constantly being introduced into 
the area in some manner that cannot be explained; and in 
many cases the new forms belong to altogether new generic 
types, which have no near allies in the older strata. This 
fact, which is, of course, one not confined to the particular 
