14 Trans. Acad. Sci. of St. Louis. 



upper Devonian faunas of New York. It also continues into 

 the faunas of the lower portion of the Mississippian series. 

 In the Devonian faunas various species are recognized, S. 

 iowensis, 8. iuUiensis, 8. impressa, etc., but they all seem to 

 merge the one into the other, the real specific lines having 

 never yet been drawn with entire satisfaction. A part or all 

 of them should perhaps be included in the one European 

 species S. striatula. The Carboniferous specimens are 

 usually called S. swallovi, though this species is perhaps 

 indistinguishable from the European 8. resupinata. 



A comparison of a large number of the later Devonian 

 representatives of the genus and the early Carboniferous ones, 

 seems to indicate that they all belong to one common stock 

 which exhibits local variations both in time and space. With 

 the progress of time the shells exhibit a tendency to increase 

 in size, a tendency which is apparently independent of the 

 environment in which the organisms lived. Not that the 

 smallest ones are always the earliest in time, but that the 

 average size of the earlier ones is less than the average size 

 of the later ones. The specimens of 8. tulliensis illustrated 

 by Hall * are all under 30 mm. in breadth, the average being 

 about 28 mm., and his illustrations may be taken as repre- 

 senting about the average size of the species. On the other 

 hand, 8. swallovi in the Osage fauna sometimes attains a 

 width of 60 mm., the average probably being between 40 and 

 50 mm. That this difference is not dependent upon the envi- 

 ronment is shown by the fact that in the Chemung fauna, the 

 highest of the Devonian faunas in New York, the species 

 8. impressa grows to a much larger size than does 8. tullien- 

 sis at the base of the Upper Devonian. One of the specimens 

 illustrated by Hall t is between 39 and 40 mm. in breadth, 

 and other specimens have been observed still larger, this in 

 spite of the fact that the Chemung environment was very 

 different from the environment in which the large Osage 

 representatives lived, and in spite of the fact that the 

 Chemung environment was not particularly favorable to 

 brachiopod life. 



* Pal. N. Y. 4. pi. VII. f. 5 a-k. t Pal. N. Y. 4. pi. VIII. /. 11-19. 



