SOME NEW DEVONIC FOSSILS 



271 



anterior margin. These are distinctly mutational characters which 

 constitute very notable differences in the shells. The surface 

 characters are more distinctly indicative of progressional phases 

 of development and may be thus tabulated for the three different 

 expressions of the species : 



Primary fascicles at the beak 3 y~ 5 P 



•' { 10-14 p r e c e d e n s, b o n a m 1 c a 



[ frequent — p recedens 

 Intercalation of striae apicad of summit -1 less frequent — p a t e r s o n i 



\ occasional — b o n a m i c a 



/finely and 

 subequally lobed — p atersoni, precedens 

 J,. 



coarsely and 

 -Strongly fasciculate — b o n a m i c a 



ii^^ 



Stropheodonta patersoni protype bonamica 



The umbonal corrugation appears to be differently developed 

 according to individuals, but generally is coarsest in precedens, 

 smaller and more numerous in p a t e r s o n i. The summarized evi- 

 dence indicates the phylogenetic relation of these species to be thus : 

 bonamica retains the most primitive expression throughout sup- 

 plemented by the character of its hinge which is denticulate only 

 near the delthyrium ; precedens is still more primitive than 

 patersoni in respect to striation, but less so than bonamica. 

 The relation indicated seems to be in accordance with the actual 

 time relations of these shells. 



Students of the Brachiopoda recognize in the fasciculate-crenu- 

 late type of surface structure a recrudescence in these early 

 Devonic shells of characters which appeared among the Stropho- 

 menoids in the Lower Siluric and except for the crenulation 

 became prevalent. This later expression is never common nor did 



