Hyatt.] 260 [April 4, 



Following out the history of these parts the Nautiloids can be 

 subdivided into the following general genetic groups, [1] Holo- 

 choanoida, those having long funnels which completely close the 

 intervals between the septa. We can subdivide this group into 

 Prochoanites, those with funnels of septa turned forwards, ex. 

 Bathmoceras, Metachoanites, those with funnels turned backwards 

 and completely closing up the walls of the siphon, which has no 

 intervening connective wall, ex. Endoceras, and Trocholites. 

 [2J Ellipochoanoida, those with short funnels and the siphon 

 completed by an intervening connective wall of distinct structure 

 from the septal funnels. 



There are many of the Orthoceratites which have funnels of 

 considerable length like those above noted as transitional to 

 Bactrites. These are, as shown by M. Barrande, directly con- 

 nected with the extremely short funneled group of the Actinocer- 

 atidae. We, therefore, divide the Ellipochoanoida into the true 

 Microchoanites, which embrace the Actinoceratidae and most of 

 the true Kautiloids, including Nautilus, and the Macrochoanites. 



The Macrochoanites may be said to include Bactrites and such 

 straight forms as are transitional to Ammonoidea and all the 

 Nautilinidae, and also the Clymeninae which have similar long 

 funnels. The advantage of this name in trying to present natural 

 relations is evident because we can thus bring all the forms which 

 are transitional from Nautiloids to Ammonoids into one group, 

 and present them under one descriptive name. In our classification 

 we have, for obvious reasons of convenience, included some of the 

 true Orthoceratites among the Macrochoanites, since there are some, 

 as we have said, which can properly be included with Bactrites. 



In the more complicated forms of Goniatitinae, while the young 

 are quite generally macrochoanitic, the later larval stages and the 

 adults are universally short funnelled. These short funnels are, 

 however, quite distinct from the short funnels of the Nautiloids, 

 and we propose to class them in with the next type to which they 

 are transitional. The collar is present in all the higher forms or 

 true Ammonitinae, and has been observed by Beyrich in one of 

 the typical Goniatitinae, and the forms possessing this modifica- 

 tion we propose to assemble under the name of the Cloiochoa- 

 nites. This collared group, therefore, correlates with the median 

 ventral saddle, which is present in all of these groups, namely all 



