BRACmOPODA. 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. 

 IVoodwardi, 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,! 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, Diyiobolus ? Hicksi, from the Upper Aienig- of St. David's (Quart. 

 Journ. Geol. Soc, vol. xxxi, p. 188, jil. x, fig-. 6. 1875 ; and Bi-itish Silurian Brach. Suppl., p. 212, pi. xvi, 

 fig. 19. 1883), but the characters of the single specimen are so obscure as to render this refei-ence 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. 



