144 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



Gen. DOSINIA Scop. 

 71. DOSINIA MAGELLANICA spec. nov. 



PI. XXVII, Fig. 13. 



1899 D. complanata Ortmann, in: Am. Journ. Sci., v. 8, p. 429 (non D. 

 complauata Phil . ) . 



Shell orbicular, compressed. Posterior dorsal margin forming, with the 

 posterior margin, a regular, circular curve. Lunula ovate, concave, but 

 elevated in the middle. Surface with regular concentric impressed lines, 

 which are not very crowded (y* to ^ mm distant from each other), dis- 

 tinct all over the shell ; intervals between these lines perfectly flat, but 

 near the anterior and posterior margins a little elevated. 



Length, 28 mm; height, 26.5 mm; diameter, about 4 (X2) mm. 



Remarks: In my first publication I made a mistake: I believed some 

 fragments of Lucina neglecta (see above, p. 130) imbedded in the same 

 piece of rock to belong to this species. But now, after succeeding in 

 working them out of the matrix more satisfactorily, I see that we really 

 have to deal with two different forms, and that the characters of the sur- 

 face markings and of the curve of the posterior and dorsal margins, on 

 which I founded the identification with Philippi's D. complanata, are taken 

 from individuals of the new Lucina. 



D. magellanica differs from D. complanata in the shell's being a little 

 more convex, in the posterior dorsal margin's forming no angle with the 

 posterior margin, and in the surface ornaments, which consist of impressed 

 lines, not of elevated striae. 



In the following species (D. meridionalis), the curve between posterior 

 dorsal and posterior margins is not regularly circular, but there is a sug- 

 gestion of a blunt angle ; the lunula is not elevated in the middle, the 

 concentric ornaments are more irregular, and the intervals between the 

 impressed lines are more or less convex ; the shell itself is much larger. 



Record of specimens : Punta Arenas, horizon II (lower Magellanian), 2 

 right, i left valves. 



Affinities: The most closely allied form seems to be: D. semilcevis 

 (Artemis s., Philippi, 1887, p. 113, pi. 13, f. 22) from Navidad, especially 

 as regards the concentric lines, which are said to be "remote" from each 



