468 THE PALEONTOLOGY OF MINNESOTA. 



[Zygosplra uphaini. 



valve with about eighteen simple, rounded plications; surface obscurely punctate." 

 Interior structure unknown. Brachial supports large, in the mature stage with 

 about five loosely coiled volutions to each spire and more or less medially directed 

 towards the dorsal valve. On the first or outermost volution on the dorsal side of 

 each spire a band is given off which is more or less backwardly curved, joining 

 medially, and thus forms the "loop" or connecting band. The point at which it is 

 given off from the spires is variable. The band may cross in front of the apices of 

 the spires or above the posterior turn of the second volution. 



In the Hudson River group this species is quite distinct from Z. recurvirostra. 

 Near the top of the Trenton in Kentucky, however, Z. recurvirostra and Z. modesta 

 are found together, but these specimens, as a rule, are typically neither the one nor 

 the other. The general expression, however, is more that of Z. modesta. In Minne- 

 sota the two species are always distinct and hold widely separated horizons. In 

 New York, associated with Z. recurvirostrr near the middle of the Trenton, is found 

 Z. deflecta, Hall,* a species in many respects like Z. modesta, showing that the tendency 

 of development of the former is toward the latter. For other remarks see Z. uphami 

 and Z. recurvirostra. 



Formation and locality. Rare in the Huson River group at Spring Valley, Minnesota. Common in 

 the same formation of the Ohio valley; Savannah, Illinois; New York and Canada. In the upper portion 

 of the Trenton and Utica slate of New York. Whitfleld (Geol. Wisconsin) gives it as occurring in the 

 Trenton, Galena and Hudson River groups of Wisconsin. 



Collectors. -E. O. Ulrich, W. H. Scofleld and the writers. 

 Mus. Beg. No. 8228. 



/ 



ZYGOSPIEA UPHAMI W. and S. 



PLATE XXXIV, FIGS. 45-48. 



1892, April 1. Zygospira uphami W. and S. American Geologist, vol. ix, p. 291. 



This species occurs in the fine-grained portions of the Galena limestone about 

 twenty feet beneath the Maclureabeds and fifty or more feet above the layers 

 containing Z. recurvirostra in abundance. Its general expression shows it to be a 

 probable descendant of Z. recurvirostra, having attained a larger size, greater con- 

 vexity and somewhat finer striae. The latter feature is more apparent than real, 

 owing to the greater size of Z. uphami. Some specimens from which the shell has 

 been partially exfoliated show the interior of the ventral valve to have a deep 

 muscular cavity extending from the beak to about one-third the length of the shell. 

 From the antero-lateral margins of this area originate two prominent, diverging 

 ridges, probably the markings of the main trunks of the vascular system; which 

 become obsolete near the front margin. The crural plates of the dorsal valve are 

 very strong and at their bases coalesce with a stout, but rather short, median septum, 

 upon each side of which, posteriorly, are situated two depressions of the adductor 

 scars, the second pair being undefined. 



Pal. N. Y., vol, i, p. 140, pi. xxxm, figs. 4a, 4b. 



