INVERTEBRATE PALAEONTOLOGY. 493 



name Cryptoceras in 1850; but d'Orbigny's name cannot stand, because 

 Barrande had used it for a genus of Cephalopoda in 1S4G. It is true that 

 Barrande subsequently changed the name of his genus to Ascoceras, because 

 Latreille had, in 1804, used Cryptocerus for a genus of insects. If this was a 

 sufficient reason, however, for changing Barrande's name, Latreille's Crypto- 

 cerus would be equally in the way of d'Orbigny's Cryptoceras ; and, if not, 

 then Dr. Barrande's genus would have to retain his original name, which 

 would render d'Orbigny's name equally untenable. 



It is very probable that Professor King intended his name Discus to 

 ripply to shells that would fall into the groups Temnochilus, Discites, and 

 Trematodiscus, as well as perhaps other sections of the older Nautili. He 

 did not define it, or cite any particular species as an example; but it is evi- 

 dent that he had in view discoid shells with volutions merely in contact, as 

 he alludes to Crioceras as only differing in having volutions not in contact. 

 At one time, Professor Worthen and 1 adopted his name Discus for the same 

 group that we subsequently called Trematodiscus ; but it is evident that Pro- 

 fessor King's name cannot stand, for the reason that it had been previously 

 used for other genera by Fitzinger in 1833 and by other authors at differ- 

 ent dates; while he published no diagnosis and cited no type. 



The name Discites had also been used by some older authors than 

 De Hann ; but, as it has not been retained for the types to which they applied 

 it, I think there is no reason why it may not be used for the section ot 

 Nautilus to which De Hann and McCoy applied it. 



The type for which Mr. Conrad proposed the name Hcrcoghssa forms 

 a transition from Nautilus proper to Aturia; that is, it agrees exactly with 

 the former in all respects excepting in the lobed character of its septa, in 

 which, as well as in form, it agrees still more nearly with the latter; but it 

 nevertheless differs from Aturia in having its siphuncle cylindrical and more 

 nearly central, as in Nautilus, and not large and funnel-shaped. 



It is not always possible to group objects of natural history in a linear 

 series, so as to bring types most intimately related nearest to each other, 

 because forms that most nearly agree in some characters will often be found 

 to differ widely in others. In most characters, Hercoglossa certainly seems to 

 approach the true Nautili more nearly than any of the other sections that I 

 have placed nearer the latter; hut, in the lobed character of its septa, it 

 diverge:; as widely from the typical forms of the genus as any of the 



