STANTON : THE MARINE CRETACEOUS INVERTEBRATES. 
13 
gular with rounded extremity and bounded below by a deep byssal sinus, 
posterior ear much smaller, with the outer margin oblique and broadly 
rounded above, both with radiating striae ; the body of the shell marked 
by rather conspicuous irregularly spaced concentric lines and by very fine 
curved radiating impressed lines. 
Height, 25 mm.; length of hinge line 11 mm.; greatest length (about 
the middle of the valve) 23 mm. 
This description is drawn from the type, a well preserved right valve, 
from the locality ten miles east of Lake Pueyrrydon. The collection from 
four miles east of the same lake contains some less perfect specimens be- 
lieved to belong to this species, and among them are two left valves hav- 
ing the same sculpture and general form as the type. These are slightly 
more convex than the right valve and the anterior ear is similar in form 
and only slightly larger than the posterior. 
The species has the typical Camptonectes sculpture and form as seen in 
a number of described Jurassic and Cretaceous species, but according to 
Dali 1 Camptonectes is not of generic or even subgeneric rank but should 
be placed as a section under Pseudamusium. 
Locality and position . — From the Ammonite (Belgrano) beds at the 
two localities above mentioned. 
Pecten argentinus sp. nov. 
Pi. IV, Fig. 5. 
Shell of moderate size, ovate in outline, very gently convex, with me- 
dian pointed beaks ; ears subequal, in the form of slender right-angled 
triangles, projecting beyond the beak at their outer angle, separated from 
the body of the shell by impressed lines that form a right angle where 
they intersect at the beak; basal margin forming almost a semi-circular 
curve ; surface smooth and polished, with very fine lines of growth, occa- 
sional more prominent impressed concentric lines, and very faint indica- 
tions of fine radiating lines. 
The figured specimen, which is of average size, is 23 mm. in height and 
21 mm. in greatest length. The corresponding dimensions of the largest 
example in the collection are about twice as great. The convexity of sin- 
gle valves is not more than two to three millimeters. 
1 Trans. Wagner Free Institute, Vol. Ill, pt. IV, p. 697, Philadelphia, 1898. 
