1878.] 35 [Rathbun. 



the North American, is the absence of radiating raised lines on the 

 former; but this is probably due to the coarse character of the rock 

 in which the specimens were found. 



Rios Maecuni and Curua. (Geol. Comm., 1876.) 

 Terebratula Derbyana Hartt, MS. 



Rathbun, Bull. Butf. Soc. Nat. Sci., l, no. 4, p. 236, pi. x, 1874. 



This species was obtained at Erere in great abundance in 1876 by 

 the Geological Commission. Specimens of larger size than before 

 known were collected by them, but none giving a clearer idea of the 

 true relations of the species. The largest specimen found measures 

 in length 14 mm., in breadth 10 mm. From the Rio Curua was pro- 

 cured a ventral valve of a small specimen of Terebratula, probably 

 belonging to this same species. 



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

 Curuii. (Geol. Comm., 1876.) 

 Tropidoleptus carinatus Hall. 



Strophomena carinata Conr., Ann. Geol. Rept. of N. Y., p. 64, 1839. 

 Lfiptcena laticosta Hall, Owen and others. Tropidoleptus carinatus 

 Hall, 10th Rep. St. Cab. N. Y., p. 151, 1857; PalaBont. N. Y., iv, p. 

 407, pi. LXii, 1867 ; Rathbun, Bull. Buff. Soc. Nat. Sci., i, no. 4, p. 

 254, pis. IX and X, 1874. 



The description of the Brazilian form, in the Bulletin of the 

 Buffalo Society of Natural Science, referred to above, was made 

 from a few specimens collected at Erere in 1871. The collection 

 made by the Geological Commission in 1876, however, contains many 

 varieties resembling more closely the species as it is known in N. 

 America. This last collection has also many very large specimens. 



The length and breadth of the younger shells are sometimes near- 

 ly equal, and the cardinal extremities are rounded or acutely angu- 

 lar. In the older forms the shell is frequently transversely subellip- 

 tical. The ventral valve is often subcarinate along the middle, the 

 carina including from one to three plications, and the central plica- 

 tion of this valve is always the larger, whether the carina exists or 

 not. The younger shells are not carinate. A depression, correspond- 

 ing to the carina of the ventral valve, usually exists in the dorsal 

 valve. The largest specimen examined has a length of 31 mm., and 

 a breadth of 42 mm.; there are also many other specimens in the 

 collection nearly equalling this one in size. 



Rare at the Erere locality. (Morgan Ex., 1871; Geol. Comm., 

 1876.) Very abundant on the Rios Maecuni and Curua. (Geol. 



