246 



[I have attached to this pretty species the name of my old friend, 

 Mr. Thos. "Ward, the explorer, of the Tocautins on the Thayer ex- 

 pedition, and one to whom I am under a deep debt of gratitude for 

 aid in my first journey to the Amazonas in 1870. — C. F. H.] 



Rliyuchonella (Steuocisma) dotis, Hall, (Palaeontology of New York, Vol. 

 IV, p. 344,) Plate VIII, figs. 10 and 12. 



Of the Erere form the ventral valve is unknown. 



Dorsal valve rather below the medium size, of moderate convexity, which is 

 stronger towards the front, quite flattened near the middle ; slightly trans- 

 verse with the greatest width midway between the beak and the front ; very 

 short-ovate in outline, slightly truncate in front, and angular behind. The 

 nearly straight posterior lateral margins diverge at an angle of about 110 de- 

 grees, and extend less than one-third the length of the valve, the lateral mar- 

 gins rounding quite strongly and regularly to the edge of the fold, in front of 

 which the margin is nearly straight. From the depressed beak the valve rises 

 quite abruptly for a short distance along the median line, and then continues 

 with a very gentle curve, or nearlj^ straight, to the front. On each side, it 

 rounds up strongly for one-fourth the width or more, and is nearly flat in the 

 middle. The mesial fold commences just anterior to the middle, and increases 

 very gradually in width, being but slightly prominent at the front. The 

 valve has about 16 plications, of which four occupy the fold. The plications 

 are prominent, varying in width, being usually rounded near the middle of the 

 valve, but becoming angular towards the sides, with the reverse plications 

 generally narrower. The first one or two on each side next the fold extend 

 nearly directly from the beak to the margin, the others, in succession, curving 

 more and more strongly outward toward the lateral margins, and decreasing in 

 size, those on the extreme sides being very small and angular. A narrow sep- 

 tum extends forward from the beak, for about one-third the length of the 

 valve. 



The most perfect specimen measures, length 11 m. m., breadth 13 m. m., 

 height about 3.5 m. m., width of fold in front about 5 m. m. 



This small species of Rliyncliondla is probably identical with R. 

 dotis, Hall, Hamilton group, N. Y. The specimens from New 

 York vary much in the character of the plications, which are some- 

 times very angular, and at others well rounded. In the Brazilian 

 specimens, so far obtained, the plications are of an intermediate 

 character. 



From the Devonian sandstone of Erere, Prov. do Para, Brazil, 

 obtained with Strcptorhijnchus Agassizii, Retzia Jamesiana, etc. 

 (Morgan Expeditions 1870 and '71.) 



