SYNOPSIS OF GENERA. 
xlv 
P, ovifrons being almost extinct), it becomes manifestly impossible to ascribe 
even a sub-generic value to such variations. 
The sub-genus Phaeton was proposed by M. Barrande, in 1846, for forms 
of Proetus in which the pygidium bears a marginal fimbria caused by the ex¬ 
tension of the annulations. 
Forbesia, McCoy, 1816 {Proetus concinnus, Dalman, type), is a Proetus in which 
but two pairs of lateral furrows have been observed. 
Celmus, Angelin, 1878 {C. granulatus, Ang., type), is founded upon an ex¬ 
ample in which there are twelve thoracic segments and but two pairs of lateral 
furrows. These last two genera are as yet imperfectly known, and may prove to 
include species showing a structure intermediate between that of the true 
Proetus and of Cyphaspis. 
Genus PHAETHONIDES, Angelin. 1878. 
183.). Asaphus {partim), Mdrchison. Silurian System. 
1845. Proetus (partim), Loven. Ofversigt. af. Kongl. Vetensk. Akail. Foi-hamli. 
1846. Phaeton, Barrande (?). Notice pidliminaire sui' les Syst. Sil. Bobeiiie. 
1847. Prionopeltis, Corda (1). Prodroin Monog. bohm. Ti-ilob. 
1852. Proetus (Phaeton), Barrande (?). Syst. Sil. Bohenie, vol. i. 
1863. Proetus ( imTtim ), Billings. Dev. and Silui-. Foss. Siiuare Lake, Me. 
1877. Proetus (Phaeton), Meek. U. S. Geol. Surv. Expl. Fortieth Parallel. 
1878. Phaethonides, Angelin. Palieontologia Scandinavica. 
1885. Phaeton, CEhlert. Bull, de la Soc. d’Etudes Scientif. d’Angers. 
Diagnosis. Cephalon as in Cyphaspis, the fron¬ 
tal area, however, being more deeply concave, 
and the lateral glabellar furrows stronger and 
generally duplicate. Thorax composed of not less 
than seven narrow segments, and probably more. 
Axis wide. Pygidium Proetoid, relatively large, 
bearing from eight to twelve annulations upon 
the axis, and eight or nine upon the pleurse. 
These annulations extend to the margin, and 
are conspicuously duplicate their entire length. 
Surface tubercled or smooth. 
