108 
PALEONTOLOGY OF NEW YORK. 
thence inward to their point of union. The stem is short, making an angle 
with the lateral branches, and is directed backward. It reaches the level of the 
crura at a considerable distance in front of them and is there bifurcated, each 
arm making a slight double or sigmoid curve. These arms are, however, too 
short to reach the umbonal blades. The stem itself is continued for a short 
distance above the point of bifurcation. The spiral ribbons make ten or eleven 
volutions in full-grown individuals. Fimbrim are absent from both the spirals 
and loop. 
Accepting this reconstruction of the loop as correct, this organ proves to be 
precisely what might be anticipated in this Devonian genus; it resembles that 
of the preexisting genera Rhynchospira and Trematospira in its position on the 
primary lainellse, its erect attitude, as well as in the slight twist in the ribbon 
near its origin, while the length of the lateral branches and the terminal bifur¬ 
cation are like Eumetria. From Rhynchospira the genus further differs in the 
presence of the split tube in the umbonal cavity, which feature seems to attain 
its highest development among these retzioid genera. There are also some 
additional differences of secondary importance in the structure of the hinge- 
plate in these two genera. 
Reizia Adrieni is, therefore, a type of distinct generic structure, of which, as 
already remarked, no other representative is at present known It is quite 
certain that the genus is not a member of the palaeozoic faunas of America, 
so far as known, the so-called Retzias of our Devonian being mostly referable to 
Rhynchospira. 
Genus RHYNCHOSPIRA, Hall. 1859. 
PLATE L. 
1852. Atrypa, Hall. Palaeontology of N. Y., vol. ii, p. 280, pi. Ivii, fig. 7. 
1857. Waldheimia, Hall. Tenth Ann. Kept. N. Y. State Cab. Nat. Hist., pp. 87-89. 
1859. Rhynchospira, Hall. Twelfth Ann. Rept. N. Y. State Cah. Nat. Hist., pp. 29, 30, figs, 1-6. 
1859. Rhynchospira, Hall. Palaeontology of N. Y., vol. iii, pp. 213-217, 484, 485, pi. xxxvi, figs. 1, 2; 
pi. xxxvi A, fig. 1; pi. xcv A, figs. 1, 7-11. 
1861. Retzia, Billings. Canadian Journal, vol. vi, new ser., p. 147, fig. 58. 
(?) 1862. Retzia, A. Winchell. Proc. Acad. Nat. Sci. Philadelphia, vol. vi, second ser., p. 406. 
1863. Rhynchospira, Hall. Sixteenth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 58, figs. 12-17. 
1863. Rhynchospira, Hall. Ti-ansactions of the Albany Institute, vol. iv, p. 213. 
1863. Retzia, Billings. Geology of Canada, p. 373, fig. 395. 
