BRACHIOPODA. 157 



modesta, (Say) Hall, Atrypa recurvirostra* and A. defleda, Hall. In the Hudson 

 River group are the species Z. modesta, (Say) Hall, Z. Kentuckiensis, James, 

 Z. Cincinnatiensis, Meek, Z. concenirica, 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. 



riu. i.o\'. 



In faunas of later date occurs the species which ^'^^'^C^ZZ^'^ 

 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. 



Sdbqends CATAZYGA, s.-gen. nov. 



PLATE LVI. 



Mr. E. Billings described,! in 1862, the species Athyris Headi, from 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 erraiica, from the sandy Hudson River 



* Me88i-8. WiKCHBH, and Schdchbrt have recently separated from the shells usually ^referred to this 

 species cei-tain larger and more finely striated shells from the Trenton and Galena horizons. These are 

 termed Zygospira Uphami. See Amei-ican Geologist, vol. ix, p. 291 (1892), and Geological Survey of Min- 

 nesota, vol. iii, p. 468. pi. xxxiv, figs. 45^8 (1893). By the favor of Prof. N. H. Winchell we have been 

 peiTnitted to refer to advanced pages of the latter work. 



t Palffiozoic Fossils, vol. 1, p. 147, fig. 125. 



