470 THE PALEONTOLOGY OF MINNESOTA. 
[Cyclosplra bisulcata. 
In Zygospira, Glassia, Dayia and Atrypa of the Atrypidce the primary lamellae 
diverge widely and have between them the spirals; but in the Spiriferidce, to which 
family Cyclospira belongs, the primary lamellae remain close together and they are 
between the spirals, except in Cyclospira. 
This type of calcareous brachial supports has heretofore not been known to 
occur in rocks older than the Upper Silurian, and it is therefore interesting to find 
a species possessing them so early as the Trenton of the Lower Silurian. In Upper 
Silurian genera of the family Spiriferidce the number of revolutions in each spiral 
cone is always numerous, while in Cyclospira it never exceeds much more than two 
turns and is therefore more rudimentary. Since the primary lamellae remain straight 
where they join the crural plates in both Clyclospira and in the* members of the 
family Spiriferidce the genus must be regarded as belonging to that family. It is 
also geologically and structurally nearer the ancestral stock which gave origin to 
the entire suborder Helicopeymata, or spire bearing families. Zyyospira, however, is 
still nearer this ancestral stock, since it is known to occur in the Birdseye and Black 
River formations; but in this genus the apices of the spirals are dorso-medially 
directed. The direction of coiling serves well enough for family distinction, but 
we believe that both types of spirals, and also the Terehratulidce, were derived from 
one stock, which probably is to be looked for in the Rhynchonellidce. Waagen,t how- 
ever, derived the f-Ami\ j Atrypidce, of which Zygospira is a member, from the Rhyncho- 
nellidce, while all the other forms of spire-bearing genera he considered as developed 
from the Terehratulidce. 
Cyclospira bisulcata Emmons, sp. ? 
PLATE XXXIV. FIGS. 49-54. 
1842. Orthis bisulcata Emmons. Geology of New York; Report, Second District, p. 396, flg. 4 (not 
described). 
1847. Atrypa bisulcata Hall. Paleontology of New York, vol. i, p. 139, pi. xxxiii, flg. 3. 
1859. Genus 9 bisulcata Hall. Twelfth Report, N. Y. State Cabinet of Natural History, p. 65. 
1877. Camarella bisulcata Miller. American Palaeozoic Fossils, p. 107. 
1892. Camarella owatonnensis SAiiBESO^i. Bulletin of the Minnesota Academy of Natural Sciences, 
vol. iii, p. 328. pi. iv, figs. 1-3. 
Original description: "Small, ovoid; dorsal [ventral] valve with a well defined, 
narrow, mesial sinus, which continues about halfway to the beak, and from there the 
center becomes much elevated ; beak of the dorsal valve strongly incurved over that 
of the oposite valve; ventral [dorsal] valve depressed-convex, prominent on the umbo, 
beak very small and abruptly incurved; front with two short, well defined furrows, 
ending in two plications, which close on each side of the projecting plait formed by 
the extension of the mesial groove of the dorsal valve." (Hall, op. cit.) 
tPal. Indica., ser. xiil, vol. i, p. 550. 
