96 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



Of these individuals Nos. 1-12 are in our collection from Punta Arenas; 

 No. 13 is Philippi's P. magellamcus, and No. 14 is Philippi's P. ibari. 

 No. 15 gives the measurements of v. Ihering's P. piihnnatus cnevensis. 



The following are the corresponding measurements of our smaller indi- 

 viduals from Santa Cruz: 



16 



17 



18 



28 

 25 

 19 



29 

 25 

 19 



9 

 8 

 6 



10 

 9 



very slightly oblique (left), 

 circular (right), 

 circular (right). 



Finally, we have here the measurements of an individual from Lake 

 Pueyrredon, base of Tertiary : 



19 | 93 90 | ca. 34 | ? ? | slightly oblique, high (left). 



Individuals from other localities are too poorly preserved to be meas- 

 ured. 



It may be, that P. colcliagiictisis Phil. (1887, p. 191, pi. 37, f. 8) from 

 the Navidad beds of Chili is identical with our species ; it is of medium 

 size, and the measurements fit well into the series, but Philippi says that 

 the surface shows only lines of growth, and hardly any radial striae ; and 

 further, the sulci of the area seem to be according to the figure more 

 numerous and more crowded. 



P. arancanus Phil, is a very young form ; Philippi says that it differs 

 from other species in the rectilinear hinge line. The same character is 

 present in a few of our smallest and medium sized specimens from Santa 

 Cruz, but it disappears with age. Although these young specimens from 

 Santa Cruz resemble completely Philippi's figure of P. araucanits, it does 

 not seem quite safe to put this species in the synonymy of P. ibari, with- 

 out having compared authentic specimens of the Navidad form. 



The failure on the part of v. Ihering to recognize the identity of his 

 species with P. inagcllanicns and ibari of Philippi, is apparently due to 

 the fact that Philippi has figured two extremes of this form ; an excep- 

 tionally transverse one, and an exceptionally high one; but we possess 

 from the type-locality (Punta Arenas) not only these two extremes, but 

 also the intermediate forms. The latter prevail, are more circular in out- 

 line, and agree well with v, Ihering's species (so especially our Nos. 4, 5, 

 and 8). 



The large specimens in our collection from Rio Chalia are all casts, but 

 agree well as far as can be ascertained with the specimens from Punta 



