BRACHIOPODA. 
157 
modesta, (Say) Hall, Atrypa recurvirostra* and A. dejiecta, Hall. In the Hudson 
River group are the species Z. modesta, (Say) Hall, Z. Kentuckiensis, James, 
Z. Cincinnatiensis, Meek, Z. concentrica, Ulrich, Z. pau- 
pera, Billings, and probably the Rhynchonella mica, 
Billings. There is still another species in this fauna 
as it is developed in Pike county, Missouri, Zygospira 
putilla, sp. nov. (see Plate LV, figs. 35-37), which 
possesses an unusually elongate form, but retains 
the coarsely plicate surface of Z. modesta; its loop 
appears to be persistently posterior in its posi¬ 
tion. 
In faunas of later date occurs the species which ot zygospira putuia . (c.) 
has been described as Z. minima. Hall, in the Niagara group at Waldron, Indiana, 
but it is exceedingly rare, and its internal structure is not known. The genus 
has not been satisfactorily identified in European faunas. 
Subgenus CATAZYGA, s.-gen. nov. 
PLATE LVI. 
Mr. E. Billings described,f in 1862, the species Athyris Headi,^Yom the Hud¬ 
son River formation on the “ south shore of the St. Lawrence, opposite Three 
Rivers.” It is a rather large, subcircular or ovoid shell, with valves more con¬ 
vex than in Zygospira, the rotundity of the pedicle-valve obscuring the usual 
prominence of the umbo in that genus. Both valves bear a low median sinus, 
while the external surface, instead of being coarsely plicated as in Zygospira, is 
covered with a great number of fine radiating striae. The typical external expres¬ 
sion of Zygospira is thus to a large degree lost. On the interior of the pedicle- 
valve the muscular impressions are well defined and similar to those seen on the 
internal casts of the Orthis? or Zygospira erratica, from the sandy Hudson River 
* Messrs. Winchell and Schuchbrt have recently separated from the shells usually j-eferred to this 
species certain lai-ger and more finely striated shells from the Trenton and Galena horizons. These ai'e 
Zygospira Uphami. See American Geologist, vol. ix, p. 291 (1892), and Geological Survey of Min¬ 
nesota, vol. iii, p. 468, pi. xxxiv, figs. 45-48 (1893). By the favor of Prof. N. H. Winchell we have been 
permitted to refer to advanced pages of the latter work. 
t Palaeozoic Fossils, vol. 1, p. 147, fig. 125. 
