STANTON THE MARINE CRETACEOUS INVERTEBRATES. 25 
ovate adductor muscle impressions. The pallial line is very faint and the 
sinus not distinctly seen. 
Length of an average specimen 20 mm.; height 9 mm.; convexity of 
both valves about 4 mm. 
This species closely resembles Solen ccqualis d’Orbigny 1 which the 
same author afterward referred to Solecurtus. It is smaller than that 
species and not quite so slender. 
Locality and position. — The figured specimen is from the Ammonite 
(Belgrano) beds 10 miles east of Lake Pueyrrydon. It also occurs at the 
locality four miles east of the lake, and is represented by about a dozen 
specimens from the two places. 
Pleuromya latisulcata sp. nov. 
PI. VI, Figs. 1 and 2. 
Shell of medium size, oblong ovate, or subcuneate in form, the great- 
est convexity near the front end midway between the beak and the ven- 
tral margin ; anterior end broadly rounded, posterior end more narrowly 
rounded and slightly gaping ; ventral margin very slightly convex ; dor- 
sal margin descending abruptly in front of the beaks and rather rapidly 
behind them ; beaks prominent, approximate, somewhat flattened, situated 
near the anterior end of the shell ; a rather prominent broad ridge, on 
which the sculpture is most strongly marked, extending from the beak al- 
most vertically to the antero-ventral angle, a much more obscure pos- 
teiioi umbonal ridge running obliquely to the posterior end, and the side 
between these two ridges flattened ; surface marked by very prominent 
concentric ribs separated by broader furrows, and the whole covered with 
finer growth lines. 
Length, 38 mm. ; height, 25 mm. ; convexity of the two valves, 20 mm. 
Locality and position. — From the Ammonite (Belgrano) beds at mouth 
of canon four miles east of Lake Pueyrrydon. Represented by a single 
specimen. 
Mactra (?) sp. 
Shell rather small, elongate, moderately convex, with prominent beaks 
slightly in advance of the middle ; anterior end broadly rounded ; posterior 
end narrow, obliquely subtruncate; ventral margin gently convex: an 
1 Pal- Fr. Terr. Cret., t. 3, p. 321, pi. 350, figs. 5-7. 
