82 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
patagomca, although the outline is more elongate, and the number of 
hinge teeth appears to be smaller. In outline, as well as the lack of cren- 
ulations, the Pliocene and Recent N. tennis (Mont.) (see Wood, 1856, p. 
84, pi. 10, f. 5) still more resembles our species, but N. tenuis is much 
thinner, and has distinctly a convex anterior dorsal margin. Thus we 
may say that, if there are any relations of the Patagonian shell to known 
forms, they are with Oligocene and Pliocene species. 
In so-called “Eocene” (or Miocene?) beds of Victoria, South Australia, 
and Tasmania, we have N. tumida Ten.-Wood (Tate, 1886, p. 127, pi. 6, 
f. 6) as a representative of N. patagonica. 
23. Nucula reticularis Ortmann. 
PI. XXV, Fig. 8“> 6 . 
1900 R. ret. Ortmann, in: Amer. Journ. Sci., v. 10, p. 371. 
Shell small, moderately convex and moderately thick, subovate, oblique ; 
posterior and anterior dorsal margins slightly convex, ventral margin 
strongly arcuate. Surface with very fine concentric ribs, which are, espe- 
cially near the posterior extremity, irregular and bifurcate. These ribs 
are crossed by still finer radial striae, which give a beautifully reticulated 
appearance to the shell. Ventral margin finely crenellated on inner side. 
Plinge teeth fine, both parts of the series forming an obtuse angle; ante- 
rior part with ca. 9, posterior with ca. 18 teeth. 
Measurements: Length, 7.5 mm; height, 6 mm. 
Remarks: The radial striae are sometimes obliterated by fossilization 
and indistinct, but are recognizable in almost all individuals on closer 
inspection. 
Record of specimens : Mouth of Santa Cruz River, 1 valve ; Mt. of Obser- 
vation, upper horizon, 16 valves. 
Affinities : The small size and sculpture characterizes this species suffi- 
ciently. This peculiar sculpture, however, brings our species very near 
to the Oligocene N. chasteli Nyst (see Sandberger, 1863, p. 342, pi. 28, f. 
7), from Germany. In N. chasteli the same dichotomy of the concentric 
ribs is present, but much more strongly pronounced, and the external form 
is different: it is triangular or hatchet-shaped. 
