1878.J 27 [Rathbun. 



and neither much elevated nor strongly incurved. Size of the largest 

 dorsal valve found; length 25 mm., breadth 33 mm. 



There seems to be no species of Spirifera in the Devonian of N. 

 America with which the form under discussion can be compared. It 

 has the appearance of a much lengthened S. duodenaria. Only 

 three sspecimens have been found, a dorsal and a ventral (?) valve, 

 in the sandstone of the Rio Msecurii, and a small dorsal one in the 

 sandstone of the Rio Curua. (Geol. Comm., 1876.) 

 Spirifera Pedroana Hartt, MS. 



Rathbun, Bull. Buff. Soc. Nat. Sci., i. no. 4, p. 237, pi. vxii, 1874. 



Collections made since the original description of this species was 

 published have furnished some new forms of Spirifera, very closely 

 related to this species, if not identical with it. From the want of 

 sufficient material to better characterize these varieties, I have 

 placed them provisionally in the species S. Pedroana. We can sepa- 

 rate the specimens into two general varieties, in the first of which the 

 ventral valve has a rather broad hinge area, very slight curvature of 

 the surface from the beak to the front margin, and also well devel- 

 oped, rather large and long, dental plates, which sometimes reach 

 nearly to the front of the valve. In the character of the dental 

 plates this variety aftproaches 5. Elizce Hartt, but it always has Avell 

 marked plications, by which the two species can be readily distin- 

 guished. In the second variety, which is connected to the first by 

 many intermediate forms, the ventral valve is much less convex, very 

 slightly curved, with the margins very regularly curved, and the 

 cardinal extremities rounded. On either side of the median sinus 

 there are at times as many as twenty-four plications, and such exam- 

 ples often resemble the flattened forms of 5. medialis, of the Hamil- 

 ton group of New York. This extreme variety may eventually prove 

 to be distinct from .S^. Pedroana. 



The localities at which the different varieties of this species have 

 been found are as follows: Devonian sandstone of Erere, very abund- 

 ant; Rios Maicurii and Curua very rare, especially the typical forms ; 

 but several odd varieties were obtained from these localities. In the 

 collection from the Curud there is a single large specimen, having a 

 width of 70 mm. At the falls of Teuapixima on the Rio Maecurii, 

 there is a fine-grained micaceous sandstone, containing S. Pedroana 

 and Rhynchonella dolis. The former occurs of small size and is usu- 

 ally quite transverse, with a thin shell. 



(Morgan Exs., 1870 and '71; Geol. Comm., 1876.) • 



