IO8 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



but with very long area). The rest are young individuals, of various 

 shapes ; one upper valve shows crenulations on the margin ; a very young 

 lower one (pi. XIX, fig. i c ) shows the corresponding grooves. 



10. 30 miles north of upper Rio Chalia ; 2 double, 6 lower, 2 upper 

 valves. 



One of the double valves is the type of my O. philippii; the lamellae 

 are on ^ of the shell remote, as in O. hatcheri. The other double valve, 

 and one of the lower ones agree with this in the elongate form and long 

 area, but the lamellae are crowded. Another lower valve is very broad, 

 almost circular, area short and broad, and it agrees in these respects with 

 O. hatcheri; but the lamellae are very crowded. The type of O. philippii 

 has distinct crenulations near the area of the upper valve. 



1 1. Canon near Sierra Oveja, Rio Chico (interstratified with Santa-Cruz 

 beds) ; i double, 2 lower, 2 upper valves. 



The double valve is the typical O. philippii, but the area is a little 

 shorter (= O. bourgeois*). Outline of the others irregularly oval, lamellae 

 not much crowded, but less distant than in O. hatcheri. Area triangular. 

 In one of the upper valves the lamellae are very distant for half its length. 



12. Shell Gap, Rio Chico, lower horizon; i double, i lower, i upper 

 valve. 



The double valve corresponds to O. hatcheri. The lower valve (pi. 

 XVII) is elongated, area very long, lamellae crowded, only near the beak 

 more distant. The upper valve is broadly ovate, the lamellae more 

 crowded than in the typical O. hatcheri. 



13. Mayer Basin, upper lignites; 2 lower valves. 

 Elongate, with long area, corresponding to O. philippii. 



14. Arroyo Gio; 2 double, 16 lower, i upper valves. 



One of the double valves is very large, round ; the other one small, 

 circular ; the latter with remote lamellae, and distinct crenulations in the 

 upper valve near the area ; it is a typical O. hatcheri, while in the larger 

 one the lamellae are more crowded. One of the lower valves is very 

 large, round, with lamellae like O. hatcheri, but the area is elongated. 

 The upper valve is an ovate, typical O. bourgeoisi, with crenulations. 

 The rest (15 lower valves) grow in clusters, of very irregular shape; no 

 characters of O. hatcheri are present ; area mostly triangular, in a few very 

 long; 4 of them show grooves corresponding to crenulations near the 

 area ; they correspond to O. bourgeoisi and philippii. 



