BRACHIOPODA. 
39 
Dinobolus Schmidti, Davidson and King, from Esthonia, Russia, as given by these 
authors, it is impossible to cite specific differences from D. Conradi; D. Cana¬ 
densis, and D. magnificus, Billings, are known only from their exterior; D. 
Woodwardi, Salter, is imperfectly understood, while D. transversus, Salter, D. 
parvus, Whitfield, and D. Bohemicus, Barrande, appear to be well defined 
species. 
The close relationship of Dinobolus to Monomerella is apparent both in the 
slight development of the umbonal cavities in the pedicle-valve, and in the gen¬ 
eral aspect of the interior of the brachial valve, the shape of its platform and 
development of its muscular scars. The differences, however, are of perma¬ 
nent value. No true platform-vaults are formed in either valve of Monomer¬ 
ella, merely a broad, general excavation of the anterior walls of the platform; 
moreover, the crescent in this genus never attains the strong and peculiar 
development seen in Dinobolus, but is more of the nature of that in Trimerella. 
The approach to Trimerella indicated by the long vaults occasionally seen 
in Dinobolus, has been referred to, but in no instance among the Trimerellas 
or Monomerellas has there been observed any tendency to a duplication of 
these vaults, as in Dinobolus. In some respects, therefore, Dinobolus stands 
as the connecting link of these two genera; or, as it was the first of the 
genera to appear in palaeozoic faunas, it may be naturally considered the 
more comprehensive type of Trimerella, Monomerella and Rhinobolus, from 
which these latter may have derived many features by easy stages of evolu¬ 
tion. 
Dinobolus makes its first appearance in the Lower Silurian, # D. Brimonti, 
Rouault,f being from the Budleigh-Salterton pebbles, and various localities in 
Brittany, of the age of the lower Llandeilo, or the Gres Armoricain; D. 
magnificus, Billings, and D. Canadensis, Billings, from the Black River limestone 
* Mr. Davidson described a species, Dinobolus ? Hicksi, from the Upper Arenig of St. David’s (Quart. 
Journ. Geol. Soc., vol. xxxi, p. 18S, pi- x > fig 1 - 6. 1875; and British Silurian Brach. Suppl., p. 212, pi. xvi, 
fig. 19. 1883), but the characters of the single specimen are so obscure as to .render this reference exceed¬ 
ingly questionable. 
t Davidson. Brachiopoda of the Budleigh-Salterton Pebble-bed, p. 365, figs. 1, 2 (p. 366), pi. xl, figs. 
22,23. 1881. 
