1883.] 271 [Hyatt. 



as having central siphon, and sutures similar to Her. (Naut.) 

 Dnnicus. The ventral saddles, and lateral saddles are broad, the 

 lateral lobes deep, but not acute. There are annular lobes in the 

 adults, but none in the young of most species. Siphon central, or 

 subcentral, but never close to the dorsum. The shells are Creta- 

 ceous and sometimes costated like those of Cymatoceras. 



Aturia, Bronn, Leth. Geog., Vol. 2, p. 1123, equal Megasi- 

 phonia D'Orb. Prod, de Pal. Vol. 2, p. 309, includes Tertiary 

 forms, with smooth and involute shells. The sutures have broad, 

 ventral saddles, acute, linguiform lateral lobes, broad, lateral sad- 

 dles, and dorsal lobes with annular lobes. The siphon is extraor- 

 dinarily large and close to the dorsum, but the funnels do not 

 affect the sutures. It seems to be truly holochoanoidal according, 

 to Barrande's and Chalmas' investigations ; and M. Barrande's 

 great authority, and comparisons of the structure of the siphon of 

 Aturia, and Endoceras led us to represent this genus as perhaps 

 belonging to the Holochormoida even in our introduction to the 

 present essay. The study of the siphon, however, in Aturia has 

 finally satisfied us that Quenstedt's figure, Die Ceph., pi. 2, fig. 23, 

 of the siphon, though imaginary, presents the typical structure 

 better than Barrande's. Aturia, therefore, has a siphon con- 

 sisting of the same elements as in the Ellipochoanoida, but with 

 such excessively long funnels, that the connective wall is reduced 

 to a minimum. It is not a reversion to the holochoanoidal 

 siphon, but a morphological equivalent, or representative of the 

 Macrochoanite forms of the early Ammonoidea, and some Nauti- 

 loids. 



ELLIPOCHOANOIDA. 



Microchoanites. 



A ctinoceratidae. 



This family includes genera of longicones and brevicones having 



the nummuloidal form of siphon, with or without rosettes, and an 



endosiphon, but the brevicones all have the rosettes 1 . The shells 



1 For convenience sake we have named the separate elements or joints of the endo- 

 siphonal deposits, rosettes, each rosette being the annular ring gathered about the 

 edges of the constriction formed by the funnel. Attention is called to the fact that 

 these rosettes are internal to the true sheath deposit, or external wall of the siphon. 



