146 Tlie American Geologist. Manii, isos 
Brachiopoda. * * * Of all these only about one hundred 
und thirty have been at all generally accepted." It should be 
stated that man}' of the synonj'ms are errors in composition and 
corrections in orthography. 
In the following list there are two hundred and sevent}'- seven 
valid genera or subgenera, a growth of more than twofold since 
the date (1877) of Dall's Index. Forty-seven families or subfami- 
lies are here recognized, while in that list there are but eighteen. 
An analysis of the table of geological distribution shows con- 
clusively that the class attained its climax of diversity during 
paleozoic time. In the lower third of the primordial, the Olenel- 
lus horizon, three of the four orders are already present, while 
the fourth originates in the lower portion of the Lower Silurian. 
Not even a single suborder was introduced subsequent to the 
Lower Silurian. Of the forty-seven families and subfamilies con- 
stituting the class, thirty-six became differentiated in the paleo- 
zoic, and of these, twenty-seven disappeared with it, while but 
nine continued into the mesozoic. Of paleozoic families, six are 
represented b}^ living species, viz. : Lingulida-, JJiscinidce, Cra- 
jiiid(e, Thecidii'da', Rliynchonellidw, and Terchratididce. 
Of the two hundred and seventy-eight genera now in use, one 
hundred and eighty-six had their origin in paleozoic seas, or two- 
thirds of the entire class, and of this great number but seven are 
known to pass into the mesozoic, viz. : Lingulct, OrhicuJoidea, 
Crania., Spiriferiiia. Athi/iis, Tcn'brafula, and Hotiiptychina. 
Besides these, Cyrtlna and Rctzia are often mentioned as occur- 
ring in the Triassic, but the species probably l)elong to other 
genera. 
In the primordial, brachiopods are not numerous. They usu- 
ally differ fundamentally from each other, and do not appear to 
have been persistent, as but four of the twenty-two genera pass 
into the Lower Silurian. In the Silurian and Devonian, the class 
is ver\' prolific in species and genera. Of the fifty-one genera 
occurring in the Carboniferous but seven are known to have sur- 
vived the break between the paleozoic and mesozoic. During the 
latter period, the spire-bearing brachiopods pass out of existence, 
while the great paleozoic suborder Thecacea is represented by a 
few small species of the Tlwcldllda which continued to be repre- 
.sented up to the present time. The TrrcJndtnUdu- had their in- 
