4 GEOLOGICAL MEMOIRS. 
ture, which he regards as increased by the employment of two or 
more specific denominations. ‘To get rid of this difficulty, and intro- 
duce a system which, he thinks, would be expressive of the relations 
of many forms, he proposes to introduce after the generic name the 
radical sign (/ _), placing beneath it the name of the fundamental 
specific form, and above it that of the form supposed to be derived 
from this by “‘mutation.”” Thus the designation (or, as the author 
calls it, “the genetic formula”) of Ammonites bifleauosus (D’Orb.) 
bifleauosus, D’Orb. 
A subradiatus, Sow. 
tus being the fundamental form, and bifleawosus the form derived 
from it by ‘‘ mutation.” 
Dr. Waagen also proposes to divide the genus Ammonites into several 
genera and subgenera, according to the length of the chamber occu- 
pied by the animal, the form of the mouth, the presence or absence 
of the operculum and its nature when present (Aptychus or Ana- 
ptychus), and the sculpture,—the outlines of the lobes being regarded 
as furnishing only secondary characters, and the general form as of 
scarcely any importance. The groups founded by him upon the 
consideration of these characters are the following :— 
would be as follows :—Ammonites »—subradia- 
Genus I. Aeocrras (Capricorni, von Buch, commencing in the 
Muschelkalk with Amm. incultus, Beyr., and including A. 
planorbis, angulatus, planicosta, &c.). 
Genus IJ. Arrerrres (the group Arietes, best represented by A. 
Bucklandi). 
Genus III. Amatruevs, Montf. (commencing in the Muschelkalk 
with Amm. megalodiscus, Beyr., and including as Jurassic 
forms A. Guibalianus, oxynotus, margaritatus, pustulatus, 
cordatus, Lamberti, &c.). 
Genus IV. Harroceras (Falciferi, Flexuosi, von Buch, Insignes, 
Discri, Denticulati, &c.), with 3 subgenera :— 
1. Harpoceras sens. str. (Liassic Faleiferi, Insignes: forms like 
A. canaliculatus, trimarginatus, &e.). 
2. Oprenia (Mexuos and Tenuilobati: A. subradiatus, A. psilo- 
discus and its allies). 
3. CExorrausres (forms allied to the Oppeliw, but with the 
body-chamber geniculate: A. genicularis, dentatus, macro- 
telus, &c.). 
Genus V. SrepHanoceras (Coronati, Planulati, Macrocephal, and 
(?) Ornati), with 3 subgenera ;— 
1. SrepHanoceras sens. str. (= Coronati and Macrocepalt). 
2. PrrispHinotes (= Planulatz). 
3. Kosmocreras (= Ornati). 
Genus VI. Asprpoceras (including A. perarmatus, bispinosus, cyclo- 
tus, &¢.). [Counr M. | 
