ORTMANN : TERTIARY INVERTEBRATES. 75 



Remarks: The radiating ribs are very variable; in some cases they ex- 

 tend almost over the whole shell, in others (and this is the most common 

 form) they begin at about the middle of the shell and run to the margins, 

 and again in other cases they are visible only near the margins. In very 

 few specimens (about half a dozen out of 81 individuals) the ribs are lack- 

 ing altogether. 



The external form of the shell varies also. It is generally wider than 

 long, often distorted (as figured by Suess), and sometimes elongated, 

 longer than wide. In the latter case it approaches closely the following 

 species ( T. patagonica], but differs in the presence of ribs. This is seen 

 in a few individuals from Lake Pueyrredon and in the specimen from the 

 mouth of the Santa Cruz River (L. 26, W . 19). This same form has been 

 sent by v. Ihering to the U. S. National Museum, labelled : Gulf of San 

 Jorge. Since T. patagonica assumes sometimes a broader form, and since 

 the ribs of T. dorsata sometimes disappear completely, it is evident that 

 both species may pass into each other, and, indeed, we possess specimens 

 in which it is very hard to say, to which one they belong. In my opin- 

 ion, both species are intimately related to each other. 



There is hardly any difference between our fossil material and the re- 

 cent form now living on the coast of Patagonia, of which Mr. Hatcher has 

 collected numerous individuals. Among the fossil forms, however, there 

 are much larger shells. The fossil New Zealand form, figured by Suess, 

 has the fold and sinus more sharply defined than any of our specimens, 

 but since there is much variation among them, as well as among the recent 

 ones (the sinus and fold being in some cases quite indistinct), there is no 

 reason for separating the New Zealandian shell from T. dorsata. 



Record of specimens: Mouth of Santa Cruz River, i sp. (Van) ; Shell 

 Gap, upper horizon, 4 sp. ; East end of Lake Pueyrredon, i sp.; Lake 

 Pueyrredon, base, 81 sp. ; Lake Pueyrredon, 600' above base, 4 sp. 



Distribution: Gulf of San Jorge (2 specimens sent by v. Ihering to the 

 U. S. Nat. Mus.); Miocene (Pareora) of New Zealand (Suess, Hutt); 

 Recent, S. America (Patagonia, Straits of Magellan, Chili) and Kerguelen 

 Islands (Dav.). 



19. TEREBRATELLA PATAGONICA (Sowerby). 



PI. XIII, Fig. 8"'" and PI. XIV, Fig. i"' 4 . 



1846 Terebmtula patagonica Sowerby, in: Darwin, Geol. Obs. S. Amen, 

 p. 252, pi. 2, f. 26, 27. 



