BRACHIOPODA. 465 



Rhytichounellii (V) ncenali. 



RHYNCHONELLA (?) NEENAH Whitfield 



PLATE XXXIV, PIGS. 35-37. 



1882. Rhynchonella neenah WHITFIBLD. Geology of Wisconsin, vol. iv, p. 265, pi. xn, flgs. 19-22. 



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 Hudson River group at Iron Ridge 

 and Clifton, Wisconsin; Savannah, Illinois, and probably also at Graf, Iowa. 

 Collector. C. Schuchert. 

 Miis. Reg. No. 8146. 



Suborder HELICOPEGMATA, Waagen. 



Family ATRYPID^E, Dall. 



Subfamily ZYGOSPIRIN^E, 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, MEEK and HAYDEN. Palaeontology 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. ii'i, 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 Spiriferidce ; 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. recurvirostra, 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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