BRAOHIOPODA. 465 
Rhyiiclioniiella (V) neenali. 
Rhynchonella (?) NEENAH Whitfield 
PLATE XXXIV. FIGS. ;e-37. 
1882. Rhynchonella neenah Whitfield. Geology of Wisconsin, vol. iv, p. 2(w, pi. xii, H^s. l'J-22. 
This species is distinguished from R. anticostiensis in being more tumid and less 
triangular, while two of the four plications on the strongly elevated median fold 
usually become obsolete before reaching the anterior margin. 
Formation and locality. — Common in the upper portion of the Hud.son River group at Iron Ridge 
and Clifton, Wisconsin; Savannah, Illinois, and probably also at Graf, Iowa. 
Collector.— C. Schuchert. 
Mus. Reg. No. 8146. 
Suborder HELICOPEGMATA, Waagen. 
Family ATRYPID^, Ball. 
Subfamily ZYGOSPIRIN^, Waagen. 
Genus ZYGOSPIRA, Hall. 
1847. Stenocisma, Hall (not Conrad, 1839). Palaeontology of New York, vol. i, p. 142. 
1862. Zygospira, Hall. Fifteenth Report, N. Y. State Cabinet of Natural History, p. 151. 
1862. Zygospira, Billings. Canadian Naturalist and Geologist, vol. vii, p. 393. 
1864. Stenocisma, Mkek and Hayden. Palaiontology of the Upper Missouri, p. 16. 
1867. Zygospira, Hall. Twentieth Report, N. Y. State Cabinet of Natural History, p. 267. 
1868, Zygospira, Meek. Geological Survey of Illinois, vol. iii, p. 377. 
1882. Zygospira, Davidson. Supplement to British Silurian Brachiopoda, p. 122. 
1882. Anazyga, Davidson. Ibidem, p. 128. 
Original description: "Shells bivalve, equilateral, inequivalve; surfaces plicate 
in the typical species; a sinus on the dorsal valve. Internal spires arranged some- 
what as in Atrypa, with a broad loop passing from the outer limbs of the spiral band 
entirely across from side to side, near to or above the center and close to the inner 
side of the dorsal valve." (Hall, 1862, op. cit.) 
It appears that Zygospira is the earliest known spire-bearing genus, and is there- 
fore very instructive. The apices of its spires are medio-dorsally directed, never 
laterally as in the Spiriferida^ ; this is the chief character by which the members of 
the family Atrypidce can be distinguished from all other spire-bearing brachiopods. 
In the earliest species, Z. reciirvirostra, the spiral cones are very loosely coiled, 
each with about three volutions, while the point of attachment of the connecting 
band is constantly near the base of the outer whorl. In Z. modesta there are four or 
five whorls to each spiral cone, but the point of attachment of the loop is variable. 
In Z. headi there are six whorls to a cone and the connecting band is in the posterior 
region. In Atrypa reticularis there is a very similar arrangement of the spirals, but 
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