55 



safely admit the establishment of more than a single order ; and the preceding 

 description of Spirula naturally tended to render it less probable that the inhabi- 

 tants of the other multilocular shells would present such discrepancies of struc- 

 ture as to justify the adoption of a second. Lamarck, however, while he con- 

 cludes rather hastily from Sph-ula, that all the multilocular shells appertain to 

 veritable Cephalopods, (evidently little suspecting the variations from their plan 

 of structure presented by Nautilus) , at the same time adopts three primary divi- 

 sions, which he characterizes according to the modifications of the shell. 

 Succeeding naturalists, by whom the Cephalopods have been especially studied, 

 have in general concurred with Lamarck in placing those multilocular shells in 

 an order apart from the naked genera : thus they form the order Pohjthalamace's 

 of De Blainville {Malacologie) , and in the system of M. de Haan, are further 

 separated from the microscopic species under the term Siphonoides {Monographic 

 Ammoniteorum et Goniatiteorum Specimen) ; which appellation M. d'Orbigny, in 

 a later and elaborate treatise on the Microscopic Cephalopods, has changed to 

 Sifoniferes, {Annales des Sciences, vii. p. 96.) The Baron Cuvier, however, has 

 not, in his arrangement of the class, ventured beyond what the details of struc- 

 ture would strictly warrant ; and in the latest edition of his invaluable work 

 ' Le Regne Animal distribue d'apres son Organisation,' he says, " Les Cephalopodes 

 ne comprennent qu'un ordre, que Ton divise en genres, d'apres la nature de leur 

 coquille." 



Of the propriety, how^ever, of considering the naked genera as constituting a 

 distinct order, there can now be little doubt : at every step, indeed, of the pre- 

 ceding description, it became necessary to denote them by a collective term, 

 since the chief points in which they differed from the Nautilus were participated 

 by them in common. It cannot, of course, be assumed that the inhabitants of the 

 chambered shells shall equally participate with Nautilus in its peculiar variations 

 from the structure of the higher order ; but until further details of the organi- 

 zation of these singular and most interesting animals are acquired, the following 

 characters of the two orders, founded on the descriptive details contained in this 

 Memoir, will probably be considered admissible. 



