1878.] 30 [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 Mecurti and Curud. (Geol. Comm., 1876.) 
Terebratula Derbyana Hartt, MS. 
Rathbun, Bull. Buff. Soc. Nat. Sci., 1, no. 4, p. 236, pl. x, 1874. 
This species was obtained at Ereré 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. tee 
Ereré. (Morgan Exs., 1870 and ’71; Geol. Comm., 1876.) Rio 
Curud. (Geol. Comm., 1876.) . 
Tropidoleptus carinatus Hall. 
Strophomena carinata Conr., Ann. Geol. Rept. of N. Y., p. 64, 1839. 
Leptena laticosta Hall, Owen and others. Tvropidoleptus carinatus 
Hall, 10th Rep. St. Cab. N. Y., p. 151, 1857; Palafont. N. Y., 1v, p. 
407, pl. xu, 1867; Rathbun, Bull. Buff. Soc. Nat. Sci., 1, no. 4, p. 
254, pls. 1x 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 Ereré 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 Ereré locality. (Morgan Ex., 1871; Geol. Comm., 
1876.) Very abundant on the Rios Mecurd and Curud. (Geol. 
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