BRACHIOPODA. 127 



Hudson River group of Cincinnati, should be thus referred. Mr. C. D. Wal- 

 COTT has described a species, T. infrequens, from a lower Devonian horizon at 

 Lone Mountain, Nevada;* and the latest representative of the group appears 

 to be the T. gibbosa, Hall, of the Hamilton group, a form which is very 

 strongly plicated, but presents no substantial generic differences from T. mul- 

 tistriata so far as its interior is known. Several other American species 

 have been referred to this genus, some of which are now known not to be 

 congeneric ( T. hirsuta and T. nobilis, Hall, of the Hamilton group) ; and others 

 which can not now be placed with precision (T. Acadia, Hall, Upper Silurian; 

 T. Matthewsoni, McChesney, Niagara group ; T. Hniuscula, Winchell, Hamilton 

 group). European investigators have not satisfactorily identified the genus 

 among their faunas. 



Genus PARAZYGA, gen. nov. 



PLATE XLIX 



1857. WaldMOtiUa, Atrypa, Hall. Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., pp. 89, 168. 



1859. Trematoiplra, Hall. Palteontology of New York, vol. iii, p. 216, pi. xxxvi, fig-. 3. 



1861. Trematospira, Hall. Fourteenth Ann. Rept. N. Y. State Cab. Nat. Hist , p. 101. 



1862. Trematospira, Hall. Fifteenth Ann. Rept. N. Y. State Cab. Nat. Hist., pi. ii, Ggs. 11-16. 



1863. Retzia, Billinos. Geology of Canada, p. 385, fig. 419. 



1867. Tretnatospira, Hall. Paljeontolog^y of New York, vol. iv, p. 274, pi. xlv, figs. 16-32. 



The well known species of the Hamilton fauna of New York, Atrypa,j or 

 TrematospiraX hirsuta, Hall, agrees with typical forms of Tkematospira in the 

 general transverse and medially sinuate character of the exterior, but differs in 

 certain details of structure sufficiently to necessitate its removal from that 

 genus. The surface markings of the exterior consist of numerous fine, rounded, 

 simple ribs, extending alike over median fold and sinus, and these are covered 

 with exceedingly fine, short, hair-like spines, not so closely set nor so long as 

 in NucLEOSPiRA. Usually these delicate spines are broken off, leaving only their 

 bases, which indicate that the spines are hollow. 



The umbo of the pedicle-valve is closely incurved and the deltidium (or coa- 

 lesced deltidial plates) which is entirely concealed by the umbo of the opposite 

 valve, is usually lost. The apical portion of the umbonal cavity bears an 



• Palseoutology of the Eureka District, p. 151, pi. iv, fig. 3. 

 t Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 168. 1857. 

 J Paleontology of Naw York, vol. iv, p. 274. 



