ORTMANN : TERTIARY INVERTEBRATES. I 1 9 
Pueyrredon, 2 casts ; Lake Pueyrredon, base of Tertiary, 4 casts ; Lake 
Pueyrredon, 6oo' above base, 4 casts ; Lake Pueyrredon, marine beds 
overlying Santa Cruz beds, 9 casts. 
Distribution : San Julian (Sow.) ; Santa Cruz, LaCueva, Jegua quemada 
(v. Ih.). According to v. Ihering, P. fissicostatis is from the Patagonian, 
P. quemcidensis from the Suprapatagonian beds. 
Affinities : A very closely allied form is P. coquimbensis Moericke 
(1896, p. 577 , pi. 13, f. 7-10) from the Pliocene Coquimbo beds of Chili, 
but in P. coquimbensis both valves are said to be almost flat, and the 
intermediate ribs are less numerous ; primary ribs 26-28. 
The following species ( P . actinodes ) is also closely related, see below. 
41. Pecten actinodes Sowerby. 
PI. XXIV, Fig. i«- 6 . 
1846 P. act . Sowerby, in: Darwin, Geol. Observ. S. Amer., p. 253, pi. 3, 
f - 33- ' 
1897 P* aci - Pilsbry, in: Pr. Acad. Philad., p. 330. 
1897 P- aci ' v - Ihering, in: Rev. Mus. Paul., v. 2, p. 227. 
Shell suborbicular. Right valve very slightly convex, almost flat ; left 
valve convex. Anterior ear much larger, that of the right valve with a 
deep byssal sinus. Sculpture of both valves consisting of 30-40 principal 
ribs, which are only slightly elevated, and not very different from the in- 
termediate ribs, of which 3-7 exist in each interval. Sometimes the in- 
termediate ribs closest to the principal ribs are a little stronger, giving a sub- 
fasciculate appearance to the principal ribs. All ribs covered with squamrn. 
Height, 1 12 mm; width, 104 mm. 
Remarks : This species differs from P. geminatus in the complete ab- 
sence of geminate ribs on both valves, in the larger number and smaller 
size of the principal ribs, and the flattened right valve. It will be re- 
marked, that the form quemadensis of P. geminatus makes in some degree 
a transition toward this species. 
Record of specimens: Cape Fairweather; 15 right, n left valves, and a 
number of fragments. 
Distribution: San Josef (Sow.); Bay de la Pava, north of Desire, and 
Punta Rosa (or Raza ?, see under discussion of Cape Fairweather beds 
below), between Santa Cruz and San Julian, Tehuelche formation (v. Ih.). 
