xlvi 
SYNOPSIS OF GENERA. 
The term Phaeton was used by M, Barrande in 1846 (Notice preliminaire sur 
le Systeme Silurien et les Trilobites de Boheme, p, 62), to include a certain series 
of Trilobites possessing Proetoid characters, but differing from the normal Pro'etus 
in having the annulations of the pygidium produced into a marginal fimbria. 
This term was at first given generic value, but subsequently reduced by its 
author (Syst. Sil. de Boheme, vol. i, p. 433, 1852), to the position of a sub¬ 
genus. The name Phaeton was long previously used by Linnaeus for a genus of 
birds, and in 1847, Corda (Prodromeiner Monographie der Bohmischen Trilobi- 
ten) made use of the term Prionopeltis for the same group. In 1878, Angelin, in 
the posthumous edition of the PalcEontologia scandinavica (part i, p. 21), referred to 
the group under the term Phaethonides, ascribing the credit of the name to 
Barrande, giving it generic value and re-defining the genus in the following 
words: 
“ Corpus latiusculum, sub-ovate, distincte longitudinaliter trilobum, testa 
laevissima, aciculata tectum. 
“ Caput semilunare, undique marginatum canaliculoque lato, intramarginali 
praeditum. Anguli capitis exteriores cornigeri. Prons ovata marginem api- 
caleni baud attingens, utrinque lobo 1 distincto basali, lineisque 2 obsoletis 
abbreviatis impressis. 
“ Oculi sat magni, semi-circulares, approximati, sub-basales. Sutura facialis 
utrinque ab oculis extrorsum flexa, postice ad latera capitis antieeque ad margi¬ 
nem apicalem ducta. 
“ Thorax e segmentis 10, sulco pleurico instructis; rachi pleuris angustiore. 
'^Abdomen majusculum, semi-circulare, immarginatum, inargine integerrimo 
ant dentato; rachis angusta, sub-cylindracea, ante scuti apiceni evanescens; 
latera scuti sub-plana, costis dichotomis.” 
As thus amended the group is made to include not only species with fimbri¬ 
ated pygidia, but also such as have the pygidial margin entire; cephala with a 
short, ovoid glabella, having distinct basal lobes and two pairs of faint, obso¬ 
lescent lateral furrows in front of the lobes. 
The type species under Angelin’s diagnosis is Asaphus {Pro'etus) Stokesi, 
Murchison, in which the pygidium has an entire margin, and the cephalon 
bears features which are more closely similar to those of the genus Cyphaspis 
