122 SUPPLEMENT TO THE 



bottom of the dorsal valve. Dr. Hinde informs me that he found it near Jupiter River, 

 Anticosti, in a Silurian rock at about the horizon of the Wenlock. 



Mr. Glass has likewise developed the spirals in a specimen of Atrypa marginalis from 

 the Upper Silurian Limestone of Anticosti, and found them to agree with those in 

 similar specimens from the Wenlock of Shropshire. 



Genus- — Spirtpera Sow., 1815. 



Spirifera Maia, Billings, sp. =:Athyris Maia, Billings. Can. Journal Ind. Sci. and 



Arts, 1860. 



Mr. Glass has opened out the interior of several specimens of this species, and found 

 them to contain spirals similar to those of Spirifera type, but of a somewhat new and 

 very elegant shape. The specimens so examined were found by Dr. Hinde in the 

 Corniferous (Middle Devonian) at St. Mary's, Ontario, Canada. 



Genus — Zygospira, Hall, 1862. 

 ^uytis, a yoke, o-TeTpa, a spire. Type Z. modesta, Say, MS.^ 



Shell bivalve, equilateral, inequivalve ; surface plicate in the typical species ; a 

 sinus on the dorsal valve. 



The primary lamellee of the spiral cones are attached to the hinge-plate of the dorsal 

 valve. After descending almost parallel to each other for a short distance, they are bent 

 outwards, nearly at right angles towards the lateral margins of the shell, and thence form 

 a broad curve to the anterior margin, where they recurve, making about four convolu- 

 tions, with the apices of the spires directed obhquely into the cavity of the dorsal valve. 

 The loop commences on each side from about the centre of the primary lamella. It 



* Atrypa modesta, Hall, ' Pal. New York,' vol. i, p. 141, pi. xxxiii, fig. 15, 1847, and 'Thirteenth 

 Annual Eeport of the University of the State of New York,' p. 69, 1800. 



Zijgospir a modesta. Hall, ' Fifteenth Annual Report of the Regents of the University of New York,' 

 1862, and 'Twentieth Annual Report,' p. 267, 1868. 



