228 F. R. Cowper Reed — On the Phacopidce. 



I. Subfamily Dalmanitin^. 



1. Genus Bnlmanites. 



Subgenera Dalmanitina, nom. prop. 



Dahnanites, sens. str. (= Hausmannia).. 



Asteropyge 



Odontocephalns 



Coriicephalus 



MaUadaia ^ = Synphoria. 



Coronura 



Froholium 



Cryphitia 



II. Subfamily PhacopinjE. 



2. Genus Phacops. 



Subgenera Phacopidella, nom. prop. 



Phacops, sens. str. (= Somatrikelon) . 

 Trimerocephalus. 



III. Subfamily PterygometopinjE. 



3. Genus Pterygometopus. 



Subgenera Pterygometopus, sens. str. 

 Chasmops. 

 Homalops. 

 Monorakos. 



The earliest and least differentiated members of each genus are- 

 comprised in the subgenera Dalmanitina, Phacopidella, and Pterygo- 

 metopus, sens, str., and being such have many features in common. 



Geographical Distribution. 



With regard to their geographical distribution, Dalmanitina occurs 

 in the northern and southern provinces of Europe in Ordovician 

 times, but Pterygometopus only in the northern. Phacopidella was 

 spread over both provinces during Silurian times,, though with 

 a slightly different type of development. 



Dalmanites, sens. str. (-Hausmannia) was almost solely a northern 

 form during the Silurian period, but during the Devonian period 

 extended also into the south. 



The various subgenera of Dalmanites in Devonian times were 

 principally developed in North America, but some are found in 

 central and southern and more rarely in northern Europe. 



Stratigraphical Distribution. 



Stratigraphically the whole of the genus Pterygometopus is con- 

 fined to the Ordovician, and it accomplished its whole range of 

 modifications within the limits of that period. 



Dalmanitina is also typically an Ordovician group. Dalmanites, 

 sens, str., though principally Silurian, ranged up into the Devonian. 

 Phacopidella is Silurian, and the typical Phacops, sens, str., appears 

 in the Silurian but reaches its maximum in the Devonian. The 

 whole family became extinct before the dawn of the Carboniferous. 



