REPORT OF THE STATE PALEONTOLOGIST 1902 1045 



seems probable that S. coralliuensis was derived from 

 a smooth form similar to S. modestus } though the chances 

 of its having been derived directly from that form are slight. A 

 type which answers more readily the requirements of a radicle 

 for this species as well as the others of this group, is Spirifer 

 p e t i 1 u s Hall of the Niagaran beds of Waldron Ind. This 

 species in the adult stage has all the characters of the young of 

 S. c r i s p u s var. simplex and S. crispus, as pointed 

 out by P.eecher and Clarke. 2 S. corallinensis and S. 

 eriensis are connected by intermediate forms. In some 

 specimens from Becraft mountain, which show the adult char- 

 acters of S. eriensis, the younger portion of the shell has 

 all the characters of S. corallinensis with narrow shal- 

 low sinus and obsolete plications. As the shell is exfoliated, it 

 is not possible to say whether or not the plications are wholly 

 absent in the young, as appears to be the case. 



The derivation of S. eriensis from S. corallinensis 

 is then very clear, this being shown by morphogenesis as well 

 as chronogenesis. In like manner it can be shown that S. 

 vanuxemi was derived from S. corallinensis by an 

 accelerated development of the plications, while the fold and 

 sinus were retarded. The most accelerated individuals of S. 

 vanuxemi have, as already pointed out, a depression along 

 the middle line of the fold which in extreme cases reaches the 

 beak. These three species, S. corallinensis, S. erien- 

 s i s and S. vanuxemi, though occurring in the late 

 Siluric beds, are all retarded in development with reference to 

 the plications, when compared with S. crispus, which was 

 derived from the same stock in the Midsiluric. In fact, these 

 late Siluric species, if not known to occur above S. crispus, 

 would be placed chronologically below or with that species 

 Regarded however as retarded types, placed in an unfavorable 

 environment, their more primitive characters are understood. 



1 Schuchert has recently pointed out [U. S. Nat. Mus. Proc. 1903. 26:413] that 

 a number of the species referred to the Cumberland Helderbergian really belong 

 to the Manlius horizon of that locality. Among these is S. m o d e.s t u s. 



2 N. Y. State Mus. Mem. 1. 1889. p.75. 



