AET. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 59 



careful consideration it was decided to extend the limits of Aluta so 

 that it might properly receive the species. While this arrangement 

 may not be altogether satisfactory, it is certainl}'' a more natural 

 position than was assigned the species by Ford, who placed it under 

 Leperditia, and later by Walcott, who referred it to Aristozoe. 



Occurrence. — Limestone in shaly slates belonging in upper part of 

 Lower Cambrian, on ridge east of the city of Troy, N. Y. ; also one- 

 half mile west of North GreeuAvich, Washington County, N. Y. 



Plesiotype.— Cat. No. 17447, U.S.N.M. 



ALUTA PRIMORDIAUS (Linnarsson) 



Plate 8, Figures 11, 12 



Leperditia primordialis Linnarsson, Kongl. Sven. Vet.-Akad. Handl., vol. 8, 



No. 2, 1869, p. 84, pi. 2, figs. 65, 66. 

 Leperditia {Isochilina), primordialis Linnarsson, Of vers. K. Vet.-Akad. For- 



handl., vol. 26, 1869, p. 196; 1875, vol. 32, pp. 15, 18, 33, 34, 37, 45. 

 "Leperditia" primordialis Wallerius, Unders. Zonen med Agnostus laevigatas i 



Vestergotland, Luud, 1895, p. 62. — Gronwall, Danmarks Geol. Unders., 



II Taekke, No. 13, 1902, p. 162. 



This Swedish species is known to the authors from numerous 

 excellent specimens which show that the species can not belong to the 

 Leperditiidae, the presence of an antero-ventrally situated node 

 being altogether foreign to any member of that family of Ostracoda. 

 The species agrees in the form of its carapace and especially in the 

 position of the main tubercle, with American Cambrian species of 

 Phyllopoda here referred to Aluta. Though easily distinguished, the 

 taxonomic value of the differences, so far as they can be determined 

 is not greater than specific. The truth of this statement will be 

 apparent when the photographic copies of Linnarsson's original fig- 

 ures on Plate 8 are compared with the figures of A. troyensis and 

 rotundata on the same plate. 



Compared with A. troyensis, A. primordialis is distinguished by its 

 less acuminate, relatively blunt, anterior extremity, less produced 

 postventral margin, by the extension of the marginal rim around the 

 postdorsal angle, the greater convexity of the valves, and finally by 

 having a dorsal furrow that is not present in A. troyensis. In some of 

 these features the Swedish species agrees better with A. rotundata, 

 but the dorsal depression is much narrower, the antero-ventral node 

 much more prominent and not ridgelike, the convexity of the valves 

 greater, and the general form more elongate. The length, as given 

 by Linnarsson, is 8.0 mm., the height 5.0 mm. 



Occurrence. — Middle Cambrian, Olenidskiffer of Linnarsson, at 

 several locaUties in the province of Vestergotland, Sweden. 



