of the Transition Formations of the Rhine. \(M 



A. priniordialis, Schl., belongs to this fifth section. It occurs 

 with other species partly appertaining to this section in the 

 transition limestone of the Hartz, near Grund ; strata which 

 have great resemblance to the limestone of the Eifel, if not al- 

 together identical with it. As the limestone of the Goniatites of 

 Oberscheld is probably yet more recent than the limestone of 

 the Eifel, it appears that we may lay down this rule, that the 

 Goniatites of this section belong only to the recent transition 

 limestone in the neighbourhood of the carboniferous limestone. 

 Notwithstanding the great analogy that exists between the 

 lobes of this and those of the following section, it is interesting 

 to perceive that we can establish for the Goniatites of the car- 

 boniferous system a difference in the lobes not very impor- 

 tent, but nevertheless very constant. 



Section VI. Carbonarii. 



The dorsal lobe is divided, only a single, lateral, angulose 

 lobe, and one lateral saddle, large and rounded. 



15. Ammonites sphdericus, Mart. 

 A. carbonarius, Goldf., L. von Buck Goniat. p. 44. PL II. fig. 9 to 9'*, 



The dorsal lobe is about as broad as deep. The middle 

 elevation does not reach half the height of the lobe. The dor- 

 sal saddle, as well as the two saddles of the middle elevation, 

 form, in uniting above, an obtuse angle. The lateral lobe is 

 single, small, not much deeper than the dorsal lobe, but has 

 rather more breadth than depth. The lateral saddle inclines 

 very gradually towards the suture ; it is as high as the dorsal 

 saddle and broader than the lateral lobe. The increase in 

 height is 0*65 to 0*72, the increase in breadth 0*7. There are 

 fourteen chambers in one whorl. The inner whorls are al- 

 most entirely enveloped, leaving an umbilicus of greater or 

 less circumference. 



Between the A. sphcericuSyMoxi.^ ?ind A. carbonarius, Gold£,, 

 there is no specific difference with regard to the form or the 

 lobes. One may observe all the gradations from the spherical 

 form to those witli a large and deep umbilicus. If there is a 

 difference in the two, it is only to be sought in the quality of 

 the shell and in the great number of the folds, which in A. car^ 



Ann. Nat. Hist. Vol. 3. No. Ifi. May \^Z9, x 



