550 



CRUSTACEA. 



[HOM. 



FIG. 1013. Holorae- 

 topus angellni. 

 Head and side 

 view. 



ward the base, flattened, crossed by 

 three symmetrical ridges; the middle 

 one is inconspicuous. Type H. eos. 

 eos, Matthew, 1885, Trans. Roy. Soc. 

 Can., p. 64, St. John Gr. 



HOLOMETOPUS, Angelin, 

 1852, Palfeontologia 

 Scandinayica. [Ety. 

 holos, entire; metopon, 

 space between the 

 eyes.] Cephalic shield 

 semicircular; glabella long, narrow, 

 convex, widened in front, separated 

 from cheeks by deep furrows ; cheeks 

 tumid ; eyes small, situated well to the 

 posterior; neck furrow distinct; facial 

 sutures curved a little outward, in front 

 of the eye. Type H. limbatus. 

 angelini, Billings, 1862, Pal. Foss., p. 95, 



Quebec Gr. or Up. Taconic. 

 HOMALONOTUS, Konig, 1825, Icones. Foss. 

 Sectiles, p. 4. [Ety. liomalos, on the 

 same level ; notos, back.] Cephalic shield 

 hyperbolic, anterior angle subacute, 

 margins rounded, surface convex ; gla- 

 bella subquadrate, short, wider poste- 

 riorly, no furrows; eyes opposite the 



FKJ. 1011 Homalonotus delphinocephalas. 



central part of the glabella, small ; 

 facial suture, from the anterior angle to 

 the margin, following, the border of the 

 margin, and curving like the letter S, it 

 reaches the eye, and by a like curve 

 passes to the posterior lateral angle ; 



thoracic segments 13, axis wider than 

 the lateral lobes, which have subtrun- 

 cate ends, with large distinct facets; 

 pygidium hyperbolic and terminating 

 in a spine. Type H. knighti. 



atlas, Castelnau, 1843, Syst. Sil., p. 20. Not 

 recognized. 



dawsoni, Hall, 1860, Can. Nat. and Geo., 

 vol. 5, p. 155, and Acad. Geol., p. 607, 

 Up. Silurian. 



dekayi, Green, 1832, (Dipleura dekayi,) 

 Monograph Trilobites, p. 79, and Illust. 

 Devon. Foss., pi. 25, Ham. Gr. 



delphinocephalus, Green, 1832, (Trimerus 

 delphinocephalus,) Monograph of Trilo- 

 bites, p. 82, and Pal. N. Y., vol. 2, p. 

 309, Niagara Gr. 



giaanteus, Castelnau, 1843, Syst. Sil., p. 20. 

 Not recognized. 



herculaneus, Castelnau, 1843, Syst. Sil., p. 

 20. Not recognized. 



jacksoni, Green, 1837, (Trimerus jacksoni,) 

 Am. Jour. Sci., vol. 32, p. 347, Up. Sil. 



knighti, Konig, 1825, Icones. Foss. Sec- 

 tiles, pi. 7, fig. 85, Low. Held. Gr. 



major, Whitfield, 1885, Bull. Am. Mus. 

 Nat. Hist., vol. 1, p. 193, Oriskany Gr. 



vanuxemi, Hall, 1859, Pal. N. Y., vol. 3, 



p. 352, Low. Held. Gr. 

 ILL^NURUS, Hall, 1863, 16th Rep. N. Y. Mus. 

 Nat. Hist., p. 176. [Ety. from the genus 

 lllsenus; oura, tail.] Body broadly ellip- 

 tical ; cephalic shield short, convex, semi- 

 elliptical ; glabella subquadrate, convex, 

 smooth, without distinct dorsal furrow; 

 palpebral lobe marginal; cheeks wide; 

 facial suture nearly vertical, slightly di- 

 verging, anterior to the eye; movable 

 cheeks wide and short; thoracic seg- 

 ments con vex, central lobe wide, lateral 

 lobes narrow, pygidium short, narrow, 

 subelliptical, convex in front, more 

 curved behind. Type I. quadratus. 



convexus, Whitfield, 1878, Ann. Rep. Geo. 

 Sur. Wis., p. 66, and Geo. Wis., vol. 4, 

 p. 203, Low. Mag. Gr. 



eurekensis, Walcott, 1885, Monogr. U. S. 

 Geo. Sur., vol. 8, p. 97, Potsdam Gr. 



quadratus, Hall, 1863, 16th Rep. N. Y. St. 



Mus. Nat, Hist., p. 176, Potsdam Gr. 

 ILL.ENUS, Dalman, 1828, ueber die Paleeaden 

 oder die sogenannten Trilobiten, p. 51. 

 [Ety. illaino, to look awry, to squint.] 

 Cephalic shield very convex and like 

 one-fourth of a sphere, with the an- 

 terior margin slightly produced; gla- 

 bella defined only as a slight convexity, 

 between subparallel lines, on the pos- 

 terior part of the shield ; eyes semilu- 

 nate, near the lateral margins smooth ; 

 facial suture makes a gentle curve from 

 the antero-lateral margin to the eye, 

 and then to the margin midway of the 

 lateral lobes of the thorax; thoracic 

 segments 9 or ten, broad ; pygidium 

 much like the cephalic shield. Type I. 

 crassicauda. 



ambiguus, Foerste, 1885, Bull. Sci. Lab. 

 Denison Univ., p. 106, Niagara Gr. 



