MUSEUM OF COMPARATIVE ZOOLOGY. 71 



No. 5. — The Fossil Oephalopods of the Museum of Comparative 

 Zoology. By Alpheus Hyatt. 



This number of the Bulletin begins a series of notices upon the 

 Cephalopoda, which' besides fulfilling the common object of similar 

 numbers already published, has some peculiar features of its own re- 

 quiring a few explanatory remarks. 



The Ammonoids, including all the Cephalopoda with serrate 1 or 

 foliated septa, the Clymeniae, Goniatites, Ceratites, and Ammonites 

 proper, are separated by Professor L. Agassiz from the Nautiloids 

 and Dibranchiate Cephalopoda as a distinct order. . 



The typical group of this order is the so-called genus Ammonites. 



De Montfort and De Ilaan both recognized a few new genera within 

 the limits of this incongruous genus before Von Buch described the 

 natural groups which continue to bear his names. Von Buch called 

 these groups '"families," but classified them under the " generic" name 

 of Ammonites ; thus plainly, although indirectly, announcing his opinion 

 of their sub-generic value. 



Professor L. Agassiz, for many years past, considered some of these 

 groups as natural families, and deemed them capable of division into 

 subordinate groups of generic importance. 



lie imparted this fundamental idea to me at the beginning of my 

 studies upon these interesting fossils, and selected the five genera which 

 are referred to his authority as examples of the manner in which I 

 should treat this subject, at the time he recommended the investigation 

 to me. Further than this, the work is my own. 



I have pursued no special method in the classification, but have 

 directed my whole attention to the verification of the groups defined 

 by Von Buch and others, and the subsequent testing of the limits of 

 the included genera by a careful comparison of all the minor divisions 

 in each natural group. 



The shells or mineral casts of every group have been first arranged 

 in series of species, and the limits of these series determined the genera. 

 The generic characteristics were selected from those peculiar to all the 

 species of each series which were not common to the family or any 

 more comprehensive division. 



