1878.] 33 [Rathbun. 



The entii-e length of tlie shell is 28 mm., width 26 mm., depth of 

 the dorsal valve 15 mm., width of fold at the front about 11 mm. 



Only a single specimen of this large species of Rhynchonella was 

 obtained; this is the cast of a dorsal valve, with a portion of the ven- 

 tral valve attached. It is readily distinguished from the other species 

 recorded in this paper, by its larger size, greater proportionate 

 length, and the moi'e extended, pointed beak of the dorsal valve. 



From the Devonian sandstone of Erere. (Geol. Comm., 1876.) 

 Ehynchonella (Stenocisma) dotis (?) Hall. 



lihi/iicfionella {Stenocisjim) dotis Hall, Pala3ont. of New York, IV, p. 

 34-i, pi. Liv, 1867; Rathbun, Bull. Buff. Soc. Nat. Sci., i, no. 4, p. 

 246, pi. VIII, 1874. 



This species was first recorded from Brazil in the report of the 

 Morgan Expeditions referred to above. At that time only two speci- 

 mens were known from the Devonian sandstone of Erere. These 

 were both dorsal valves, which agreed quite closely in their charac- 

 ters with Rhynchonella dotis of the Hamilton group of New York. 

 The Geological Commission discovered no more specimens of this 

 species at Erere; but in the sandstone beds of the Rios Msecurii and 

 Curua were found many specimens of Rhynchonella, representing 

 several varieties, of which the most are closely connected together 

 and to the Erere variety, by intermediate forms. Some of the varie- 

 ties, however, present differences which may necessitate their being 

 separated eventually from the commoner form. The result of the 

 studies made on these varieties of Rhynchonella indicate that this 

 species from Bi'azil may prove to be as closely related to some other 

 of the N. American species as to R. dotis; but I was unable to make 

 comparisons with a sufficiently large collection, and thus it has 

 seemed best to retain the species as it is for the present. 



As a rule, the shell of the Brazilian form is more or less trans- 

 verse, or has the length and breadth nearly eciual. Ventral valve 

 short-ovate in outline; dorsal valve very short-ovate or transversely 

 subelliptical. Of the ventral valve the beak is small, quite sharply 

 pointed, and strongly incurved. The posterior margins diverge at an 

 angle of about 105° to 115°, and are nearly straight. Anterior mar- 

 gin broadly, but not deeply, indented by the sinus. The surface of 

 the valve is generally much flattened toward the front, and curves 

 rapidly downward toward the front and lateral margins. 



Dorsal valve very convex, the surface rising regularly an<l rapidly 

 from the beak to near the anterior margin, toward which it curves 



fUOCEEDIXGS B. S. X. H. — VOL. XX. 3 JANUARY, 1879. 



