12 M. E, Beyrich on the Goniatitea 



that happens almost constantly) does not increase in the 

 same proportion as the breadth. For this reason I have en- 

 tirely neglected its determination; moreover, for the distinc- 

 tion of the several species, we must not attach to these nume- 

 rical proportions a greater degree of importance than they 

 really deserve. If, in general, questions concerning organic 

 bodies cannot be mathematically determined, we may with 

 still greater reason in the present instance disregard little 

 discrepancies ; dealing as we are with fossils, the imperfect 

 preservation of which seldom permits a great degree of accu- 

 racy of admeasurement. 



Section I. Nautilini. 



The dorsal lobe simple, infundibuliform or linguiform; there 

 is one single lateral lobe, smooth and rounded, which sometimes 

 disappears entirely. 



1. Ammonites subnautilinus, Schlotth. 



A. Nceggerathi, Gold/, and Von Buck, Goniat. PL I. fig. 6 — 11. 



? A. evexus, L. von Buck, Goniat. p. 33. PL I. fig. 3 — 5. 



The dorsal lobe infundibuliform ; depth equal to two or 

 three times the breadth. The lateral lobe is large, occupying 

 the whole extent of the side, it even descends nearly the whole 

 depth of the dorsal lobe, and returns towards the suture, w T ith 

 a somewhat greater inclination, to the height of the dorsal 

 saddle*. The increase in height is 0'5 to 0*55 ; the increase 

 in breadth 0*68 to 0*72 ; there are 14 chambers in one com- 

 plete whorl. The number of whorls is 6 or 7 : the inner 

 whorls are almost entirely enveloped, never more than one 

 fourth of them being perceptible. 



M. von Buch has already observed, that the A. Nceggerathi, 

 Goldf., does not essentially differ from the A. subnautilinus, 

 Schl. In these two Ammonites the lobes have a form alto- 

 gether similar ; the height and the breadth scarcely differ, and 

 the somewhat less complete involution of A . Nceggerathi will 

 scarcely suffice to constitute a variety : still less can the more 

 discoid form of the latter be regarded as a distinctive charac- 

 ter. We must be very cautious in the appreciation of the ex- 

 terior form, and in the use of that characteristic for the di- 



* The word saddle is used to denote those separations between the lobes 

 upon which the mantle of the animal is supposed to have rested. For fur- 

 ther explanation see Dr. Buckland's Bridge water Treatise, page 363, note. 



