468 THE PALEOTSTTOLOGY OF MINNESOTA. 
IZygospira uphanii. 
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. itphami 
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. Whitfield (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. Reg. No. 8228. 
Zygospira 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 recurvirostra in abundance. Its general ex^jression 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, pfobably 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. xxxiii. Ciis, 4ii, 4b. 
