44 NEW YORK STATE MUSEUM 



Stropheodonta patersoni Hall protype bonamica Clarke 



Plate 9, figures 1-6 

 See pt i, p. 186 



Stropheodonta patersoni Hall protype bonamica Clarke. N. Y. State Mas. 

 Bui. 107. 1907. p. 270 



We have noted on a previous occasion the difference in the Grande 

 Greve form of S. patersoni and the typical expression of the species 

 in the Onondaga limestone of New York. In the shell before us we have 

 a quite different expression of this type, rare in American waters. The 

 type itself, we may briefly reiterate, is expressed in the highly convex form, 

 the strong fasciculation of the striae and the corrugation of the umbonal 

 portion of the valves. We are here presented with a relatively small and 

 quite narrow shell with a short, straight hinge, prominent cardinal extremi- 

 ties, highly convex or gibbous curvature (ventral valve) and greatly produced 

 anterior margin. These are distinctly mutational characters which consti- 

 tute 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: 



i) • t ■ 1 .. .1 1 1 ( IQ— 2 ^ patersoni 



rnmary fascicles at the beak - - - J ' , , 



J I 10-14 precedens, bonamica 



1 frequent — precedens 



Intercalation of the striae apicad of summit - less frequent — patersoni 



I occasional — b o n a m i c a 



» • 1 I finely and subequally lobed — patersoni, precedens 



Anterior slope - ' , j .. 1 r 1 : 1 • 



1 ( coarsely and strongly tascicuiate — b o namica 



The umbonal corrugation appears to be differently developed according 

 to individuals, but is generally coarsest in precedens, smaller and more 

 numerous in patersoni. The summarized evidence indicates the phylo- 

 genetic relation of these species to be thus: bonamica retains the most 

 primitive expression throughout supplemented 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-crenulate type 

 of surface structure a recrudescence in these early Devonic shells of charac- 

 ters which appeared among the Strophomenoids in the Lower Siluric and 

 except for the corrugation became prevalent. This later expression is never 

 common nor did it last long. The typical S. (Orthis) interstriatus 

 Phillips is shown by Davidson 1 to carry at times the umbonal corrugations 



1 Monogr. Brach. 85, pi. 18, fig. 15—18. 



