OSTEACODA. 681 



Moore a.l 



among Ohio and Manitoba specimens, the ventral connection between the inner and 

 marginal ridges is obsolete. 



The Minnesota specimens, although from a much lower horizon than the types, 

 cannot be distinguished from them even as a good variety. 



Formation and locality. — Galena shales (Nematopora beds), near Caurion Palls, Minnesota; upper 

 beds of the Cincinnati or Hudson Elver formation at Oxford, Ohio, and Stony Mountain, Manitoba. 



Genus MOOREA, Jones and Kirkby. 



Moorea, Jones and Kiekby, 1867. Quart. Jour. Geol. Soc, vol. xxiil, p. 494; 1869. Ann. Mag. Nat. 

 Hist., ser. 4, vol. ill, p. 225, and 1886, ser. 5, vol. xviii, p. 261; 1887, Proc. 

 Geol. Assoc, vol. ix, p. 508. 



Carapace very small, more or less oblong or ovate, with the valves compressed, 

 rather thick shelled, smooth, punctate or granulose, and bounded by a raised 

 marginal ridge; the ridge may be developed only at each end, or it may continue 

 all around. Within the marginal ridge, the flat or gently convex surface shows no 

 trace of a sulcus, pit, nor of lobes. 



Types: M. obesa and M. tenuis Jones and Kirkby. 



This genus is now for the first time recognized in Lower Silurian rocks, and 

 two of the species to be described fairly illustrate the characters of the genus. The 

 third, M.? perplexa, is of doubtful affinities. A fourth species, M. smithii, has been 

 described by Prof. T. Rupert Jones from the Wenlock. This seems to be a question- 

 able Moorea, the carapace being too convex and blunt at the ends, while the ridge» 

 which should be submarginal, is here central and bifurcated posteriorly. A fifth 

 species, M. kirkbyi, described from the Corniferous limestone of Ontario by the same 

 author, is not far removed from M. angularis, while in the sixth M. hicornuta TJlrich, 

 from the Hamilton, the anterior end bears two spines. M. granosa TJlrich, from the 

 Chester group of Kentucky, is peculiar in having a granulose marginal ridge and a 

 rounded subcentral spot outlined by a row of minute papillae. The original types 

 are from the Carboniferous rocks of southern England. 



All these species are distinguished from Kirkbya, Jones, certain species of which 

 they greatly resembly, by the absence of a central pit. Some also resemble Placentula 

 Jones and Holl, and certain species of Bollia, but the first of these genera has a small 

 dorsal loop and sulcus, while the latter always has a horseshoe-shaped ridge of which 

 no trace is to be observed in Moorea. The valves in the new genus Macronotella are 

 more convex and without the marginal ridge. 



