of tlie Transition Foi'mations of the Rhine. 157 



the red limestone of the Oberscheld. Neither the increase of 

 the height or breadth can be determined from this fragment, 

 the breadth of the side upon the portion of the fragment pre- 

 served, amounts to nearly an inch and a half, so that this am- 

 monite must have been of very considerable size. The fourth 

 dorsal saddle is situated nearly at the middle of the side. 



The following Goniatites belong to the fourth section ; they 

 are from the Fichtelgebirge, A, contiguus, A. speciosus, A. sub- 

 armatus, and A. spurius, Miinster, probably also A. maximus, 

 of which the lobes are not yet known. 



Section V. Primordiales. 



The dorsal lobe is divided. There is but one lateral lobe, 

 which is generally rounded ; more rarely pointed, its ventral 

 side is raised quite to the suture, without bending itself round 

 to form a lateral saddle. , 



10. Ammonites cequabilis, n. s. PL II. fig. \, a, b. 



The dorsal lobe is more than twice as broad as it is deep. 

 The two sides in consequence rise very gradually to the dorsal 

 saddle. The middle elevation w^hich separates the two divi- 

 sions of the dorsal lobe is rounded above, does not even attain 

 half the height, and is somewhat hollowed near the siphuncle. 

 The dorsal saddle is broad and rounded, and extends forward 

 as far as the middle of the side ; the lateral lobe is nearly as 

 broad as the dorsal saddle and descends somewhat deeper than 

 half the height of the dorsal lobe ; its ventral side ascends ra- 

 pidly towards the suture, to an equal height with the dorsal 

 saddle. The increase in height is 0*7^ the increase in breadth 

 0*75. The number of whorls is from five to six, half the in- 

 nermost ones being enveloped. The height increases more 

 slowly in this ammonite than is generally the case with 

 Goniatites. The breadth also increases slowly, so that the 

 form is very discoid. The outer whorls are but little ele- 

 vated above the inner ones, which are nearly half enveloped); 

 on this account they lie together, forming almost an even sur- 

 face. The greatest thickness is at the middle of the side, 

 which abates gradually towards the back and towards the su- 

 ture. The back is rounded ; the shell thick, presenting faint 



