REPORT OF THE STATE PALEONTOLOGIST 1902 1041 



rounded at the bottom, and somewhat narrower than is usual 

 in this species. It is flanked by about four rounded plications 

 on each side, which widen gradually toward the front of the 



shell. The brachial valve has four 

 plications on each side of the central 

 fold, the fourth being very short and 

 much fainter than the others. The 

 Fig. 5 spirifer vanuxemi, median depression along the top of 



pedicle valves _ . i . 



the fold is marked in some cases, in 

 others it does not occur at all. The plications, as well 

 as the sinus and fold, extend to the apex. So far as I 

 have been able to examine specimens of S. vanuxemi 

 typical of the Manlius of eastern New York, the de- 

 pression in the median fold of the brachial valve, where it 

 occurs, is a feature of maturity rather than characteristic of 

 the entire shell. In a few cases the depression in the fold can 

 be traced nearly or perhaps quite to the apex of the valve. 

 When the depression is well marked, the plications appear 

 sharper and comparatively narrower. They also extend farther 

 up the beak. On the other hand, it appears to be the case that, 

 when the depression in the fold is faint or absent, the plications 

 are less defined and near the apex become obsolete. Neverthe 

 less, there are individuals in which the depression in the fold 

 and the broadly rounded plication occur together. Finally, 

 individuals occur (as figured by Hall) in which the apical por- 

 tion is free from plications, these beginning part way down. 

 In this case they are, so far as observed, broad and rounded. 

 The young individuals of the species are in all cases marked 

 by less pronounced and fewer plications. In certain forms, 

 which may be considered the more primitive representatives of 

 the species, the young are practically free from plications, or 

 if these occur, they are broadly rounded and low, one or two 

 only occurring on each side of the fold or sinus. From these 

 considerations we arrive at the conclusion that the ancestral 

 type from which S. vanuxemi was derived, was a pauciplicate 

 if not nonplicate form. Furthermore, that those individuals 

 among the species which have few and low plications, with a 



