ORTMANN : TERTIARY INVERTEBRATES. 159 



The taper of the young shell is apparently more considerable than in 

 the old : a fragment 29 mm long is, on the one end, 3 mm in diameter, 

 on the other, 5.5. Another one, 58 mm long, is on one end 7 mm 

 in diameter, on the other 10 mm: this latter fragment thus increases 

 only 3 mm, where we should expect at the rate of the first one about 

 5 mm. 



In D. giganteum Sowerby (1846, p. 263, pi. 2, f. i), and Philippi (1887, 

 p. 105, pi. 12, f. 9), from Navidad, the sculpture is different, consisting of 

 shallow and narrow grooves, separated by rounded and low intervals. 



According to the figure, D. sulcosum of Philippi (pi. 12, f. 10), 

 from Navidad is certainly different from D. sulcosum of Sowerby, and 

 it closely resembles D. giganteum, but the furrows are much deeper 

 and more distinct. The specimens, however, mentioned by Philippi 

 from Santa Cruz as belonging to D. sulcosum, belong no doubt to the 

 true D. sulcosum. 



D. lebuense Philippi (1887, p. 106, pi. 12, f. 18), from Lebu and Llan- 

 cahue resembles a young D. sulcosum, but it is much straighten 



D. gayi Philippi (Matanzas and Carauma), comes no doubt into the 

 synonymy of D. sulcosum : the figure resembles exactly a young individual 

 of the Santa Cruz species. 



D. patagonicum of Rochebrune and Mabille, and v. Ihering, is certainly 

 identical with our species : we have received from v. Ihering a fragment 

 of medium size under this name, and this agrees completely with our D. 

 sulcosum. 



D. mantelli Zittel (1864, p. 45, pi. 13, f. 7), from New Zealand, Victoria 

 arid South Australia (Tate, 1887, b, p. 190), and Tasmania (Pritchard, 

 1896, p. 126), comes very near to D. sulcosum. The only difference (ac- 

 cording to the figure) is the much stronger curvature of the shell. (Tate, 

 1887, b, p. 191, says : D. giganteum of which solidum Hutton is a synonym 

 is distinct though conspecific with D. mantelli, a sentence that is not quite 

 clear.) 



Record of specimens : Mouth of Santa Cruz River, 59 fragments ; San 

 Julian, Darwin Station, 2 casts ; Lake Pueyrredon, base of Tertiary, i 

 broken and compressed specimen. 



Distribution: Santa Cruz (Phil., Roch. & Mab., v. Ih.), Patagonian 

 formation (v. Ih.) ; Navidad beds of Chili : Navidad, Huafo Island (Sow.), 

 Ancud, Llancahue, Tubul, Matanzas, Carauma (Phil.). 



