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. liniuscula, Winchell, Hamilton 
group). European investigators have not satisfactorily identified the genus 
among their faunas. 
Genus PARAZYGA, gen. nov. 
PLATE XLIX. 
1857. Waldheimia, Atrypa, Hall. Tenth Ann. Kept. N. Y. State Cab. Nat. Hist., pp. 89, 168. 
1859. Trematospira, Hall. Palaeontology of New York, vol. iii, p. 216, pi. xxxvi, fig. 3. 
1861. Trematospira, Hall. Fourteenth Ann. Kept. N. Y. State Cab. Nat. Hist, p. 101. 
1862. Trematospira, Hall. Fifteenth Ann. Kept. N. Y. State Cab. Nat. Hist., pi. ii, figs. 11-16. 
1863. Retzia, Billings. Geology of Canada, p. 385, fig. 419. 
1867. Trematospira, Hall. Palaeontology of New York, vol. iv, p. 274, pi. xlv, figs. 16-32. 
The well known species of the Hamilton fauna of New York, Atnjpa,-\ ov 
TrematospiraX hirsuta, Hall, agrees with typical forms of Trematospira 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 
* Palaeontology of the Eureka District, p. 151, pi. iv, fig. 3. 
t Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 168. 1857. 
t Palaeontology of New York, vol. iv, p. 274. 
