470 THE PALEONTOLOGY OF MINNESOTA. 



[Cyclospira bisulcata. 



In Zygospira, Glassia, Dayia and Atrypa of the Atrypidw the primary lamellse 

 diverge widely and have between them the spirals; but in the Spiriferidtc, 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 Helicopegmata, or spire bearing families. Zygospira, 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 Terebratulidce, were derived from 

 one stock, which probably is to be looked for in the Rhynchonellidce. Waagen,f how- 

 ever, derived the family A trypidw, 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 Terebratulidce. 



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. Palaeontology of New York, vol. i, p. 139, pi. xxxiu, 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 SAIIDESON. Bulletin of the Minnesota Academy of Natural Sciences, 



vol. iii, p. 328. pi. iv, flgs. 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.) 



. Indica., sor. xlii. vol. i, p. 550. 



