ORTMANN I TERTIARY INVERTEBRATES. 8 1 



Remarks: V. Ihering says (in N. tricesimd] : "posterior" margin with 

 8, "dorsal" margin with 1517 teeth, a statement that certainly contains 

 an error. But it is impossible to find out what is meant, since his figure 

 27 is quite insufficient ; but so far as can be seen, the number of hinge 

 teeth does not materially differ from that observed in our specimens. 



N. tricesima is apparently the same species as N. patagonica. The 

 external form in our individuals is variable : some are a little more elon- 

 gated, others higher. Philippi figures only the cast, which is, of course, 

 more elongated, since the shell, and especially the swollen apex, is gone, 

 which detracts considerably from the height of the shell. V. Ihering fig- 

 ures, in figure 21, a very high individual (Alt. 14, Long. 15), while his 

 figure 27, which seems to represent another individual, is less high (12 by 

 14). In our specimens I have measured the following dimensions: 



Height 13 Length 16.5 Diameter 10 (of both valves) 

 15 16.5 5.5 (one valve) 



12.5 15 8 (both valves) 



For N. patagonica v. Ihering gives in 1899: 14, 17, 11, respectively. 



Our second individual corresponds very closely to N. tricesima of v. 

 Ihering, while the other two approach more or less the dimensions of N. 

 patagonica. Moreover, there are numerous intermediate specimens. 



Record of specimens : Mouth of Santa Cruz River, 20 sp. ; Lake Pue- 

 yrredon, 600' above base, i cast. 



Distribution: Santa Cruz (Phil.), Patagonian formation (v. Ih.). Su- 

 prapatagonian beds of La Cueva (N. tricesima v. Ih.). 



Affinities: N. arancana Phil. (1887, p. 198, pi. 41, f. 7) from Lebu 

 and Navidad is closely allied, and perhaps not specifically distinct ; but 

 it is too imperfectly known to decide this question. 



European Eocene species, which may be compared with N. patagonica 

 in size and outline, are : N. parisiensis Desh., bronni Desh., mixta Desh., 

 greppini Desh. ; but they have all crenulations on the ventral margin, 

 and the number of hinge teeth is larger. The same is true of N. mag- 

 nifica Conr. from the Eocene of Alabama, and of N. micletis L. and 

 mayeri Hoern. from the Miocene and Pliocene beds of Europe. The 

 character of the lack of crenulations, however, is shown in an Oligocoic 

 species of Europe, N. peregnna Desh. (see Speyer, 1866, p. 42, pi. 5, f. 

 3-5), and this species seems to be the species most closely allied to N. 



