XXXVl 
SYNOPSIS OF GENERA. 
1877. Acidaspia, Walcott. Twenty-ninth Kept. N. Y. State Mus. Nat. Hist. 
1878. Acidaspis, Kay.ser. Fauna sell. Devon. Ablag;. cles Harzes. 
1879. Acidaspiis, Hall. Trans. Albany Inst., and Twenty-eighth Kept. N. Y. State Mus. Nat. Hist. 
1879. Acidaspis, Walcott. Thirty-first Kept. N. Y. State Mus. Nat. Hist. 
1879. Acidaspis, Novak. Studien an Hypostomen i. 
1881. Acidaspis, Hall. Eleventh Ann. Re^it. Geol. Surv. Indiana. 
1883. Acidaspis, Novak. Zur Kennt. bohin. Ti'ilob. 
1884. Acidaspis, Novak. Studien an Hypostomen ii. 
1885. Acidaspis, Zittel. Handb. d. Palaiontologie. 
1885. Acidaspis, Schmidt. Revision d. Ostbalt. Silur. Ti-ilob. 
1887. Acidaspis, Foerste. Bulletin Denison University. 
Diagnosis. Body depressed-convex. Sur¬ 
face ornamented with numerous spines. 
Cephalon indistinctly trilobate, with two 
longitudinal furrows crossing the glabella, 
produced by the union of the inner ex¬ 
tremities of the three pairs of lateral fur¬ 
rows. Occipital ring conspicuous. Thorax 
with from nine to ten segments, each one bearing a strong, nonsulcate ridge 
on the pleurm, which is produced into a long, hollow spine. Pijgidium short, 
small; axis bearing from one to three annulations, and the pleurae usually but 
a single one. Margins spiniferous. 
Family, LicHADiE. 
Genus LICHAS, Dalman. 1826. 
1821. Entomostracites, Wahlbnberg. Nova Acta Soc. Sci. Upsala. 
1822. Trilobites, Schlotheim. Nachtr. Hi zur Petrefacktenkunde. 
1822. Paradoxides, Brongkiart. Hist. Nat. Crust. Fossiles. 
1825. Paradoxides, Bigsby. Jour. Acad. Nat. Science. 
1826. Asaphus, Dalman. Ueber Palseaden. 
1826. Lidias, Dalman. Ueber Palseaden. 
1828. Amjjyx, Dalman. Arsberatt. 
1829. Lidias, Holl. Handbuch der Petrefacktenkunde. 
1833. Paradoxides, Green. Monograidi of the Trilobites of North America. 
1835. Lidias, Bronn. Lethsea geognostica. 
1837. Ampyx, Hisinger. Lethsea Suecica. 
1838. Platynotus, Conrad. Ann. Rept. Pal. N. Y. 
1839. Arges, Goldfuss. Nova Acta Acad. C. L., XIX. 
1840. Paradoxides, Milne-Edward.s. Hist. Nat. Crustaces. 
1842. Asaphus, Conrad. Jour. Acad. Nat. Science. 
1842. Arges, D’Archiac and Db Vbrneuil. Trans. Geol. Society.- 
