EEMAIIKS ON THE GENUS AUCELLA. 227 



in which they are usually found obscures that feature iu a large majority of the speci- 

 meus which are collected. These shells iu their general shape so much resemble small 

 examples of Jnoceyamun that they have been frequently referred to that genus by 

 authors and collectors when their distinguishing generic features have been obscured 

 as before mentioned ; but when their full characteristics are visible they are of course 

 found to be without the transversely g^ooved hinge area and prismatic shell structure 

 which characterize Inoceramus. 



The genus AuceUa has been recognized in certain of the Mesozoic rocks of both the 

 northern and southern hemispheres, but its remaius have been found far more abun- 

 dantly in the former than in the latter part of the world, and they seem to be usually 

 more prevalent in high northern latitudes than farther south. Indeed, so far as I 

 ain aware, this genus has been recognized at only two localities in the southern hem- 

 isphere, one being upon the northern island of New Zealand' and the other in the prov- 

 iuce of 8ergipe, iu Brazil.^ In both these cases the recognition of the genus has not 

 been so complete aud satisfactoxy as could be desired, because of the imperfection of 

 the only specimens discovered. Still, there seems to be no reason to doubt the correct- 

 ness of its identification in either case. In the former case tiie specimens studied by 

 Professor von Zittel seem to have been few as well as imperfect and in the hitter case 

 only two or three imperfect examples were discovered. Therefore the following re- 

 marks will refer mainly to those forms which have been obtained from the rocks of 

 the northern hemisphere and referred to AiiccUa under various specific names. 



The geographical distribution of J. ifccZZa iu the uorthern hemisphere is circumpolar, 

 extending far to the eastward in certain regions, and it has beeu found at numei'ous 

 localities aud in great numbers. Its known north and south range iu the J)orthern 

 hemisphere is from far within the Arctic Circle to about latitude 45° in western Asia, 

 to southern India, and nearly to latitude 35° in North America. It was first known in 

 the vicinity of JMoscow,^ when it was referred to the genera Inoceramus and Mi/filiis, aud 

 afterward in Petschora Land,^ when Keyserling proposed the generic name by which 

 it is now known. Subsequently it was discovered ui)ou the eastern shore of the Caspian 

 Sea,' in northern Siberia," upon Nova Zembla," S[)itzbergeu" and Kuhn" Islands (the 

 latter lying near the east coast of Greenland), in southern India, as already mentioned,'" 



'Karl A. Zittel: Reise tier osterreiclilsclien Fregatte Novara. Goologisclier Theil, vol. 1, part 2, 

 Palaeont., p. 32, PI. VIII, Figs. 4, a, b, c. 



"' C A. White: Coutribuii.'oes li Palaeontologia do Brazil (iu bothPortugiicso aud EiiglisL), Aicliivos 

 do Museu nacioiial do Rio de Jaueiro, vol. 7, p. 50, PI. Ill, Figs. 11, V2, and 13, 



" Fischer Do WaldUciin : Oryctograpbie du gouveniemeut de JIoscou, p. 177, PI. XIX, Fig. 5. and PI. 

 XX, Figs. 1, 2, and 3. 



■"A. Kcysorliug: Wissenschaftliche Beobachtungon auf eiuer Reiso in das Potscliora-Laud, pp. '297- 

 3U1, PI. XVI, Figs. 1-17. 



■'■£. Eichwald: Geoguost.-palaeout. BeiDerkungen iiber die llalbiusc-l MangischlaU und die aleut- 

 ischeu luselu, p. 53, PL VI, Figs. 10 aud 11. 



" Middeudorff: Reiso in den aussersteu Nordcu und Osteu Siberieiis, vol. 1, No. 1, p. 255. 



' S. A. TulU)Cig: Biliang till kongl. svensk. Vet.-Akad. Haudl., voi. G, i)p. 1-24, PI. 11, Figs. 9-18. 



'G. Liud.stioiii: Om trias-ocli Juraforsteningarfrau Spetsbergeu, Kongl. sveusk.Vot.-Akad. Haudl., 

 vol. 6, No. G, p. 14, PI. Ill, Figs. 3 aud 4. 



9F. Toula: Die zweite deutscbe Nordpolarfahrt, vol. 2, pp. 41(7-505; also, Feildeu aud de Ranee: 

 Quart. Jour. Geol. Soc. London, vol. 34, 1876, p. 56. 



'"F. Stoliczka: Pal. ludica, vol. 3, p. 404, PI. XXIII. 



