THE TERTIARY DEPOSITS OF BRAZIL. 83 
proper series for comparison, it would be wrong to do more than 
give it a name for the purpose of recognition; the strong ridge, 
acute umbo, and longitudinal lines clearly determine it to be a 
Dreissena. 
Dr. C. L. F. Sandberger, in his exhaustive work ‘ Die Land- und 
Stisswasser-Conchylien,’ names many species of Dreissena ; but none 
appear to agree with our form; the extremely acute and curved umbo 
and strong keel in our species distinctly separate it from the forms 
figured by Sandberger; his D. claviformis mostly resembles our spe- 
cimen, but the ventral ridge is much more strongly marked than in 
his species. 
Loc. Canama. 
ANISOTHYRIS CARINATA, Conrad, loc. cit. p. 196, t. 10. f. 7; H. 
Woodward, loc. cit. p. 106, t. 5. f. 6. 
This singular shell is without question the same as Conrad’s Pa- 
chydon carinatus, which is so well described by Conrad and Wood- 
ward, op. cit., that it needs no notice from myself. It evidently is 
an abundant shell in these Amazonian beds. 
Loc. Canama. 
ANISOTHYRIS TENUIS, Gabb (Pachydon), American Journal of Con- 
chology, vol. vi. p. 196, t. 10. fig. 1. 
Pachydon tenua, Gabb, ib. vol. iv. p. 199, t. 16. fig. 6. 
This shell is described and figured in the American Journal above 
quoted under the name Pachydon. Conrad suggested the name Ani- 
sothyris for this genus, the name “ Pachydon” being preoccupied. 
Dr. Woodward adopts Anisothyris in his paper on the Tertiary shells 
of the Amazon valley, where the affinities and differences are also 
ably discussed. 
Loc. Canama. 
Anisoruyris Hauxweti1, H. Woodward, loc. cit. p. 105, t. 5. f. 7. 
There is no doubt this is the shell referred to in Dr. Woodward’s 
paper, closely as it resembles A. tenwis. 
Loc. Canama. 
AntsorHyRis (Pacnypon) tumipA, Ether. (PI. VII. fig. 2.) 
Shell thick, tumid, obtusely triangular, equivalve, inequilateral, 
delicately wrinkled, with a shining epidermis; posterior area 
slightly flattened; anterior region nearly vertical or obtusely 
rounded; ventral margin much rounded; umbonal region thick ; 
umbones incuryed, contiguous ; lunular area deep. Cardinal tooth 
deltoid, acute at the apex, and slightly erect ; hinge-pit deep; lateral 
tooth thick, clongated ; pallial impression simple ; oral and anal scars 
placed very far forward and backward. 
The umbonal region differs from that of Corbula in the spiral 
arrangement of the umbones, which are much incurvyed, and by the 
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