Hyatt.] 256 [April 4, 



only occurring in the Devonian and Carboniferous, and the 

 umbilical perforation is reduced to a mere depression on either 

 side of the broad neck of the protoconch. 



The siphon is so near the venter that the funnel invariably 

 breaks the continuity of the sutures with a slight lobe. The 

 funnels of the siphon are not sirmple continuations of the septa, 

 except in the Nautilinidae, and most forms of Goniatitinae. In 

 some Goniatitinae, and all other Ammonoidea, a collar is formed 

 around the siphon in addition to the funnel, the collar" being open 

 and directed forwards. 



The sutures are entire in most of the Goniatitinae, but in 

 some species of the higher and later occurring carboniferous 

 Goniatitinae marginal lobes and saddles begin to be formed, and 

 in nearly all the remaining genera of later periods, these are char- 

 acteristic. There are two lateral lobes which arise in the Goniati- 

 tinae by gradation from the simple lateral lobe of the ISTautilinidae 

 and in the higher forms an indefinite number of auxiliary lobes 

 and saddles. The ventral lobe is undivided only in the Nautil- 

 inidae, and in all other series of forms there is a median saddle, 

 the sutures of this invariably divided by a minute funnel lobe. 1 



The dorsal or inner side is occupied by a saddle in the Nautil- 

 inidae as is the case very generally among the lower forms of the 

 different series of ISTautiloids, all the remaining Goniatitinae have 

 a broad dorsal lobe, which is divided by small saddles as in 

 the exceptional forms of the Nautiloidea. 



The annular lobe is absent among the Nautilinidae, as it is also 

 universally in the lower forms of the different series of Nautiloids. 2 

 It is present, but undivided, in the remaining Goniatitinae, and is 

 divided by a median saddle only in the higher forms after the 

 expiration of the Paleozoic. 



The appearance of a decided dorsal lobe correllates usually with 

 the closer coiling of the whorls and the development of an impressed 

 dorsal zone. This enables us to see, that the impressed zone is due 

 to coiling, and also to define the gyroceran and nautilian forms. 



1 I have found some rare exceptions, adult stages of abnormal varieties with con- 

 tinuous sutures over the venter as in the young of some Ammonites, Embryology 

 of Ceph., Bull. Mus. Comp. Zool., Vol. in, p. 110, fig. 1. These facts show that we 

 are right in calling the minute central lobe on the venter, the funnel lobe. 



2 Except some of the Endoceratidae according to Dewitz. 



