1878.) 25 [Rathbun. 



broarler than in the Erere forms; but there seem to be no other 

 differences of importance. 



This species is the most abundant one in the Devonian sandstone 

 of Erere. It is nearly equally common in the sandstone of the Rio 

 MaBcuru, but only a few very small specimens were brouglit from the 

 Curua. (Morgan Exs., 1870 and '71 ; Geol. Coram., 1876.) 

 Strophodonta perplana Hall. 



Strophomena perplana Conr., Jour. Acad. Nat. Sci., viii, p. 257, 



1842. Strophomena plaristriata Conr., idem., p. 259. Strophomena 

 delthyris Conr., idem., p. 258. Strophomena crenistria Hall, Rept. 

 Fourth Geol. Dist. N. Y., p. 171, 1843. Strophomena (Strophodon- 

 ta) fragills Hall, Tenth Rept. State Cab. N. Y., p. 143, 1857. 

 Strophodonta fragilis Hall, Rept. Geol. Survey of Iowa, p. 496, 1858. 

 Strophodonta perplana Hall, Palaeont. New York, iv, pp. 92 and 

 98, 1868. 



This common species of the Devonian of New York State, ranging 

 there through the Upper Helderberg, Hamilton and Chemung 

 groups, occurs very abundantly in the Devonian sandstones of the 

 Rios Maecurii and Curua, and in these localities undergoes many of 

 the variations peculiar to it in N. Y. It sometimes attains a very 

 large size. ( Geol. Comm., 1876.) 

 Spirifera duodenaria (?) Hall. 



Delthyris duodenaria Hall, Geol. Rept. 4th Dist. N. Y., p. 1 7 1 



1843. Spirifer duodenaria Hall, Twelfth Rept. State Cab. N. Y., 

 p. 88, 1859. Spirifera duodenaria Billings, Canadian Jour., p. 256, 

 1861; Geology of Canada, p. 372, 1863; Hall, Palaeont. N. Y., iv, p. 

 189, 1868. 



The commonest species of Spirifera at the Rio Maecurii locality is 

 one which belongs very near to Spirifera duodenaria, if it is not 

 identical with it. The Brazilian variety is sometimes more trans- 

 verse than S. duodenaria, of New York. The plications of the shell 

 are generally of the same size, but are sometimes smaller. The 

 ventral sinus is of more uniform size in the Brazilian, than in the 

 American variety, and seldom becomes as broad at the front. The 

 cardinal extremities are never much flattened in the dorsal valve, 

 and never at all in the ventral, though this portion of the valve is 

 almost always smooth. The depressions intervening between the 

 plications are generally narrower than the plications themselves, 

 and are regularly rounded. The hinge-area is narrow as in S. duo- 



