EEMARKS ON THE GE^'US AUCELLA. 231 



sphere, with perhaps the exception of the species from southern India. If that view 

 is to be accepted withont qualification, some one only of the various names which have 

 been proposed must be selected to designate that widely variable species. A common 

 custom among naturalists in such cases is to take the specific name first used or pro- 

 posed by the author of the genus, which is finally recognized as the true one. But I do 

 not think the judgment of subsequent naturalists who have availed themselves of con- 

 stantly increasing knowledge should always be hampered by rigid rules of this kind 

 I have therefore selected the specific name concentrica to be used in ordinary cases, 

 because the form to which that name is applied appears to have been the first one dis- 

 covered and also because it is more generally prevalent than the one to which Keyserling 

 gave the name jyaUasii, although he placed the latter name first under the genus Aucella. 

 Bat in referring now to the various forms here illustrated I shall use the names which 

 the different authors have applied to them. 



The figures on PI. Ill are mostly copies of those which represent the different 

 forms that have been recognized in Europe, together with those from southern India, 

 Xew Zealand, and Brazil. Those upon PI. IV represent North American forms, a part 

 of them being copies of figures previously published and a part having been prepared 

 for this occasion. 



PLATE III. 



Fig. 1. A copy of Keyserling's figure of Aucella concentrica, from Reise in (las Petschora-Laii<l, I'l. 

 XVI, Fig. ir>. 



Figs. 2 aud 3. Copies of Keyseiliiig's figures (loe. cit., Figs. 13 and 14), reprcsentiug A. concentrica 



var. sublavis. 



Figs. 4 and r>. Copies of Keyserling's figures of A. crassicoUis (loc. cit., Figs. 9 aud 11). 

 Figs. 6, 7, and 8. Copies of' TuUberg's figures of A. mosqucnsis, from Nova Zembla (Bihaug till 

 kongl. svensk. Vet. Akad. Handl., vol. 6, PI. II, Figs, llj, 17, aud 18). These figures are regarded by 

 Tulfberg as representing the form which Keyserling gave as the type of J. mosqiiensis. Keyserling fig- 

 ured onTy the right valve of one example, aud, as the left valve was not illustrated, several authors be- 

 sides myself have hitherto regarded A. mosqiiensis as having a more elongate form. Specimens having 

 the beak of the left valve so short and so slightly prominent as is shown by TuUberg's figures have not 

 often been observed in North American strata. 



Fig. 9. A copy of one of Keyserling's original figures of his A. pallasii (loc. cit., Fig. 4). The ra- 

 diating lines shown ou this figure are ofteu, but not always, observable on this form. They are some- 

 times observable on the other forms, but are mure often absent. 



Figs. 10 and 11. Opposite views of a specimen in the U. S. National Museum from the vicinity of 

 Moscow. It appears to belong to the form A. pallasii. 



Figs. 12 aud 13. Opposite views of another example from near Moscow, presented to Dr. Becker 

 by Professor Holzapfel. It may perhaps be regarded as a variety of A. pallasii, although some authors 

 would probably regard it as quite as near to A. mosqaensis. This uucertaiuty of specific recognition 

 by different authors is of itself an indication of the instability of all the forms which have been des- 

 ignated as species. 



Figs. 14, 15, and Ki. Copies of Professor von Zittel's figures of his A. plicata from New Zealand 

 (Reise der osterreiehischen Fregatte Novara, Geol. Theil, vol. 1, part 2, Paleont., p. 32, PI. VIII, 



Figs. 4, o, b, c). T. , ■ 



Figs. 17 and 18. Copies of original figures of A. bra:iUtnsie White (Contribuifoes d Palaeontologia 



do Brazil, Archivos Museu nac. do Rio de Janeiro, vol. 7). The narrow, rough seam along the middle 



i>f Ihe figure is a niiueral vein, aud not a uatnral feature of the shell. 



Figs. 19 and 20. Copies of Stoliozka's figures of his A. parra (Pal. ludica, vol. 3, PI. XXXIII, 



Figs. 2a aud 3). 



PLATE IV. 



Figs. 1 and 2. Copies of Gabb's original figures of his Inoceramiia [Aucella] Piocltii (Geol. Survey, 

 California, Palaiontology, vol. 1, PI. XXV, Figs. 173 and 174). 



