xlvi SYNOPSIS OF GENERA. 



The term Phaeton was used by M. Barrande in 1846 (Notice preliminaire sur 

 le Systeme Silurien el les Trilobites de Boheme, p. 62), to include a certain series 

 of Trilobites possessing Proetoid characters, but differing from the normal ProUus 

 in having the annulations of the pygidium produced into a marginal fimbria. 

 This tenn was at first given generic value, hut subsequently reduced by its 

 author S\ st 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 1817, Corda (Prodromeiner Monographic der Bohmischen Trilobi- 

 ten) made use of the tenn Prionopeltis for the same group. In 1878, Angelin, in 

 the posthumous edition of the Paheontologia scandinavica (part i, p. 21), referred to 

 the group under the term Pha/fhonides, 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. 



" Ca/iut serailunare, undique marginatum canaliculoque lato, intramarginali 

 proeditum. Anguli capitis exteriores cornigeri. Frons ovata marginem api- 

 calein baud attingens, utrinque lobo 1 distincto basali, lineisque 2 obsoletis 

 abbreviatis impressis. 



" On//i sat magni, semi-circulares, approxiinati, sub-basales. Sutura facialis 

 utrinque ab oculis extrorsum flexa, postice ad latera capitis anticeque ad margi- 

 nem apicalem ducta. 



" Thorax e segmentis 10, sulco pleurico instructis ; rachi pleuris angustiore. 



'■'■Abdomen majusculum, semi-circulare, immarginatum, margine integerrimo 

 aut dentato; rachis angusta, sub-cylindracea, aute scuti apicein 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 (Proitus) Stokesi, 

 Murchison, in which the pygidium has an entire margin, and the cepbalon 



irs features which are more closely similar to those of the genus Cyphaspis 



