I 1 2 PATAGONIAN EXPEDITIONS '. PALAEONTOLOGY. 



Out of 14 lower valves in our material, about 10 show these radial ribs 

 of the outer surface distinctly, the rest indistinctly or not at all. The 4 

 lower valves sent by v. Ihering do not show them. 



Our individuals are small or of medium size. The largest lower valve 

 measures: Length, 135 mm; width, 79 mm; the largest upper valve: 

 Length, 142 mm; width, 91 mm. 



O. ferrarisi is nothing but the young of this species. O. remondi of 

 Philippi is certainly this species ; the lower valve figured by him shows 

 radial folds of a character that is never found in O. ingens, but frequently 

 in O. patagonica, and Philippi expressly states, that the margin of the 

 upper valve possesses crenulations ("margine interne exquisite denticu- 

 late"). These crenulations are wanting in Philippi's O. ferrarisi, and 

 therefore I consider his specimens of this species to belong to O. ingens, 

 while his figure is a copy of d'Orbigny's O. ferrarisi = patagonica. 



O. remondi of Moericke is apparently the same as O. remondi Phil. O. 

 tramitoria of Hupe and Philippi is doubtful (see above). But O. transi- 

 toria of Moericke is certainly identical with O. patagonica, since it has 

 crenulations ("deutliche Kerbung am Schalenrande"). 



O. patagonica seems to be the descendant of O. ingens. The crenula- 

 tions of the margin begin to develop in O. ingens, but are rare there, only 

 in the Cape Fairweather form they are more frequent. But they never 

 extend all around the margin. In the true O. patagonica this character is 

 fully developed, and as it seems is always present, unless obscured or 

 destroyed by the process of fossilization. 



Record of specimens: San Julian, Darwin Station, above Patagonian 

 beds; 14 lower, 33 upper valves. (V. Ihering has sent to Princeton from 

 Parana, Entrerios: i double, 3 lower, i upper valves.) 



Distribution: Entrerios ; Punta Gorda (mouth of Uruguay) ; Rio Negro ; 

 San Julian (d'Orb.). Santa Rosa (or Punta Raza?, see under discussion 

 of Cape Fairweather beds below), between Santa Cruz and San Julian, 

 Tehuelche Formation (v. Ihering, p. 225) ; Parana, Entrerios (v. Ih.). 



Pliocene of Chili : Coquimbo (Phil.), Caldera (Moer.). 



