i8 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
Locality and position . — From the Ammonite (Belgrano) beds ten miles 
east of Lake Pueyrrydon, represented by a left valve, an internal cast, 
and the imprint of the exterior of another one. 
LeDA (?) CORBULIFORMIS Sp. 110V. 
PI. IV, Fig. II. 
Shell small, elongate-ovate, rather ventricose, with prominent, tumid 
submedian beaks ; dorsal margin descending almost equally before and 
behind the beaks ; anterior end broadly rounded ; posterior end more 
narrow, subtruncate and very slightly upturned at the extremity ; ventral 
margin gently convex ; surface marked by relatively coarse, regular con- 
centric lines. 
The type measures 10 mm. in length, 7 mm. in height and 6 mm. in 
convexity of the two valves. 
The description is drawn from a single specimen which retains most of 
the shell of the left valve and shows the internal cast of the right. Im- 
pressions of small nuculoid hinge teeth are faintly shown. The reference 
to Leda is based on the form of the shell and is somewhat doubtful. 
Locality and position . — Ammonite (Belgrano) beds at mouth of canon 
four miles east of Lake Pueyrrydon. 
Trigonia subventricosa sp. nov. 
PI. IV, Figs. 19 and 20. 
Shell rather large, sublunate, inflated and broadly rounded in front, 
much contracted and considerably produced behind ; beaks prominent, 
near the anterior end ; ventral margin very convex and prominent in its 
middle third, where the strongest costae terminate, in front passing imper- 
ceptibly into the anterior margin by a more gentle curve, and behind 
passing almost straight or with a slightly concave curve toward the pos- 
terior end ; dorsal margin concave ; area rather narrow, convex, divided 
above the middle by a narrow groove, with inconspicuous lines of growth, 
not bounded by distinct carinae ; escutcheon also nearly smooth, large, 
- deeply excavated, bearing only faint costellae, that near the front are very 
short, directed backward very obliquely from the area, while toward the 
posterior end they become somewhat larger, more nearly transverse, pass- 
ing entirely across the escutcheon and sometimes curving forward near 
