582 Karl A. Grönwall. 



(I'Orb. and related species : Pr. corrugatiis M'Coy, Pr. lineatus Waag., 

 Pr. tenuistriatiis Vern., Pr. simensis Tschern. — and to his opinion 

 respecting the relationship of these forms to each others. In 1908 

 (p. 220) he classifies both Pr. tenuistriatiis Vern. and Pr. simensis 

 Tschern. as varieties of Pr. Cora d'ORB. and denies Tschernyschew's 

 assertion that Pr. Cora d'ORB. is a species characteristic of the Upper 

 Carboniferous. I cannot, of course, express any opinion on this 

 matter, but, supported by the statements before me, I should like to 

 point out that Tsghernyschew (1902, pp. 626—628) gives Pr. simen- 

 sis as belonging to the Schwagerina horizon in the Urals, while 

 Grüber (1908, p. 220), mentions it from the Lower Carboniferous in 

 southern Tian-Schan. Consequently, if Gröber's identification of 

 these two forms is correct, this form is of little importance for a 

 closer determination of the niveau of these strata. 



The related Pr. Cora is, in Beeren Eiland, found in the Cora 

 limestone, and, in Spitzbergen, in the Cyathophyllum limestone 

 (WiMAN, p. 69), and, possible, in the mosquensis limestone (Holte- 

 DAHL, 1911, p. 34). 



N:o 21. Pröductus cancriniformis Tschern. 



PI. XXVIII, Figs. 19—22. 

 Pr. cancriniformis Tschemnyschew 1889, p. 283, PI. 7, Figs. 32 — 33. 



— Schellwien 1892, p. 22, PI. 8, Figs. 20—21. 



— Diener 1897: Part III, p. 25, PI. 4, Figs. 6—7. 



— Diener 1897: Part IV, p. 31, PI. 1, Figs. 7—10. 



— Schellwien 1900, p. 43, PI. 9, Figs. 1—6. 

 Tsghernyschew 1902, p. 292, PI. 52, Figs. 5-6. 



The available figures show that this species varies pretty con- 

 siderably, both with respect to the form of the shell, the proportion 

 between length and width, the arching of the dorsal valve, and the 

 occurrence of a sinus. Our specimens are all fairly large and attain 

 at least the same size as those figured; the width, too, of the shell 

 is fairly considerable, and almost agrees with the broadest of the 

 specimens previously figured. The ventral valve is almost spirally 

 involute and presents a fairly evenly arched curve; in this respect 

 our specimens agree best with Diener's (1897 : Part IV) figures of speci- 

 mens from the Himalayas, although, on the other hand, Diener re- 

 marks that, in his material, broad forms are rare. The specimen 

 given in Fig. 19 presents an indication of a sinus, something like 

 that shown in Schellwien, 1900, PI. 9, Fig. 4. The other specimens 

 have the shell evenly arched. The dorsal margin and the ears are 

 not perfectly preserved, but there is nothing that indicates variations 

 from the typical form. The same may be said about the sculpture. 



