ORIGIN AND CHARACTERISTICS OF SUBORDERS. é 
The depressed semi-lunar whorl appears first in the adults of Anarcestes. It 
is subsequently found in the young as a stage immediately succeeding the more 
cylindrical whorl of the gyroceran stage, when that occurs. In very close-coiled 
forms, the latter may be omitted, or be only slightly indicated, and then the 
anarcestian whorl appears at the beginning of the apex. In fact, this tendency 
in Latisellati, and especially in Angustisellati, affects the shape of the protoconch 
which is excessively depressed in the embryos of the higher suborders. 
We have, therefore, considered it convenient to designate the anarces- 
tian form of whorl as the primary radical of the Ammonoidea, reserving the 
terms primitive and transitional radicals for the straight and gyroceran modi- 
fications as they appear in Bactrites and Mimoceras. 
The different series of the Clymenine and Goniatitine, and the Arcestine, 
often begin with, and maintain persistently in full-grown shells, the primary 
radical form. The Ceratitinee, Lytoceratines, and Ammonitine, on the contrary, 
have this depressed form but rarely, except in their protoconchial stage, — 
and at the beginning of the apex or true conch, while it remains in what we 
have called the goniatitic stage of development. 
The Clymeninx of the Devonian begin, when zovlogically arranged, with 
discoidal forms having depressed semi-lunar anarcestian whorls. These de- 
pressed whorls are exchanged in the higher forms for compressed discoidal 
whorls, and these in turn for compressed involute whorls. The suborder 
includes several genera and in each there occur examples. of this mode of 
succession, or rather procession, of forms, forming parallel series. 
The sutures of the genera Beneckia, Longobardites, Lecanites, Norites, 
Meekoceras, Hungarites, and Carnites show them to be true Ceratitine. We 
should, with our present information, be disposed to include these, and all 
the genera mentioned by Mojsisovics as belonging to his group of Ammonites 
trachyostraca, in the Ceratitina, distinguishing them by their well-known and 
peculiar sutures from the Arcestine, Ammonitine, and Goniatitine. 
The more or less compressed whorl, which in section can be described as 
helmet-shaped, is the natural successor of the depressed anarcestian whorl both 
in the growth of individuals and in the evolution of series of species. We have 
considered this in the work quoted, therefore, as the secondary radical. 
The secondary radicals? are prevalent in the Ceratitine, as shown by the 
extensive researches of Mojsisovics in the remarkable and masterly treatise 
above quoted. They completely replace the primary radicals as generators 
of series in the Trias, except in the paleozoic survivors of the suborder 
Arcestins. So far as the sutures are concerned, however, the Ceratitine, 
though distinctly characteristic of the triassic faunse, are like the Goniatitine. 
The young of Longobardites is really a Goniatite, similar to Prolecanites, 
1 Genera of Fossil Cephalopods, Proc. Bost. Soc. Nat. Hist., XXII. p. 812. 
* We formerly included (Gen. Foss. Ceph., p. 324) in secondary radicals some quadragonal whorls like 
those of the adults of Xenodiscus; but we are now disposed to consider this an error, arising from not hay- 
ing observed that the young of these forms often possessed, during earlier stages of growth, the secondary 
or helmet-shaped whorl. This evidence shows that, in the most ancient periods as well as in later times, 
quadragonal whorls were derivative modifications of the compressed helmet-shaped secondary radicals. 
