CRUSTACEA. 



557 



MICRODISCUS, Emmons, 1856, Am. Geol., p. 

 116. [Ely. mikros, small; diskos, quoit.] 

 Subelliptical ; cephalic shield semicir- 

 cular ; glabella narrow, convex, rounded 

 in front, more or less pointed behind, 

 without furrows or occipital groove; 

 cheeks more or less convex, no eyes or 

 trace of sutures ; thorax with four ar- 

 ticulations, axis narrow, convex, lateral 

 lobes wider, depressed; pygidium 

 shorter than the cephalic shield, sub- 

 trigonal or rounded posteriorly, tri- 

 lobed, axis divided into four or six seg- 

 ments, and having a border. Type M. 

 quadricostatus. 



connexus, Walcott, 1887, Am. Jour. Sci. 

 and Arts, 3d ser., vol. 34, p. 194, Up. 

 Taconic. 

 dawsoni, Hartt, 1868, Acad. Geo., p. 654, 



St. John Gr. 

 lobatus, Hall, 1847, (Agnostus lobatus,) 



Pal. N. Y., vol. 1, p. 258, Up. Taconic. 

 meeki, Ford, 1876, Am. Jour. Sci. and 

 Arts, 3d ser., vol. 11, p. 371, Up. Taconic. 

 parked, Walcott, 1886, Bull. U. S. Geo. 

 Sur. No. 30, p. 157, Up. Taconic. 



pulchellus, Hartt, 1885, 



x^JBtes^ Trans. Roy. Soc. Can., 



/ ffeNv P- 74, St. John Gr. 



F ifwi 1* pulchellus var. precursor, 



|FjP Matthew, 1885, Trans. 



gs Roy. Soc. Can., p. 75, 



St. John Gr. 



quadricostatus, Emmons, 

 1856, Am. Geo., p. 116, 

 Up. Taconic. 

 speciosus, Ford, 1873, 

 Am. Jour. Sci. and 

 Arts, 3d ser., vol. 6, p. 

 137, Up. Taconic. 

 NILEUS, Dalman, 1826, Uber die Palaeaden 

 Oder die Sogenannten Trilobiten, p. 49. 

 [Ety. mythological name.] Cephalic 

 shield twice as wide as long, convex, 

 lateral angles broadly rounded ; gla- 

 bella subquadrate, undefined anteriorly, 

 no lateral furrows, convex, sloping in 

 all directions from the central part; 

 facial sutures in front, nearly parallel 

 with, and almost reaching, the anterior 

 margin, each forming a sigmoid flexure 

 to the anterior part of the eye, then 

 forming a semicircular eye-lobe from 

 the posterior angle of the eye, and di- 

 rected laterally to the posterior margin 

 within the broadly rounded 

 angle of the cephalic shield ; 

 eyes very large, lunate, with 

 many lenses ; eight thoracic 

 segments, indistinctly trilo- 

 bate, axial lobe the broader ; 

 pygidium twice as wide as 

 long, not trilobate, no seg- 

 ments, broadly rounded 

 posteriorly. Type N. ar- 

 madillo. 



affiuis, Billings, 1865, Pal. 

 Foss., vol. 1, p. 275, Quebec Gr. or 

 Up. Taconic. 



FIG. 1033. Micro- 

 discus quadri- 

 costatus. Mag- 

 nified 5 diam. 



macrops, Billings, 1865, Pal. Foss., vol. 1, 

 p. 273, Quebec Gr. or Up. Taconic. 



scrutator, Billings, 1865, Pal. Foss., vol. 



1, p. 274, Quebec Gr. or Up. Taconic. 

 Nolhozoe, Barrande, Whitfield referred some 

 ovate bodies found in the Potsdam 

 sandstone, without characteristics, to 

 this genus, under the name of Nothozoe 

 vermoutana. See Bull. Am. Mus. Nat. 

 Hist., 1884, vol. 1, p. 144. 

 Nuttainia, syn. for Trinucleus. 



concentrica, see Trinucleus concentricus. 



sparsa, syn. for Homalonotus dekayi. 

 Oduntocephalus, Conrad, 1840, Am. Geo. Rep. 

 N. Y. Not properly defined. 



selenwm, see Dalmanites selenurus. 

 Odontochile, syn. for Dalmanites. 

 OGYGIA, Brongniart, 1822, Hist. Nat. Crust. 

 Foss., p. 28. [Ety. mythological name.] 

 Flat or slightly convex ; cephalic shield 

 semicircular ; glabella wider in front, 

 with three lateral furrows on each side ; 

 eyes large, lunate, affixed centrally near 

 the glabella, facial suture marginal in 

 front, curving like the letter S, and 

 terminating posteriorly midway be- 

 tween the outer angle of the cephalic 

 shield and thoracic axis; thorax with 

 narrow axis, pointed pleura;, 'grooved, 

 obscure, and remote fulcrum; eight 

 segments; pygidium many segments, 

 sides with radiating furrows, the inter- 

 stices of which are divided by half rays. 

 Type O. guettardi. 



klotzi, Rominger, 1887, Proc. Acad. Nat. 

 Sci. Phil., p. 12, Potsdam Gr. 



parabola, Hall & Whitfield, syn. for Ba- 

 thyuriscus productus. 



problematica, Walcott, 1885, Monogr. 

 U. S. Geo. Sur., vol. 8, p. 63, Potsdam Gr. 



serrata, Rominger, gyn. for Olenoides 

 nevadensis. 



producta, Hall & Whitfield, see Bathyu- 

 riscus productus. 



spinosa, see Olenoides spinosus. 



vetusta see Asaphus vetustus. 

 Olenellus, Hall, 1862, 15th Rep. N.Y. St. Mus. 

 Nat. Hist., p. 86, syn. for Elliptocephala. 



asaphoides, see Elliptocephala asaphoides. 



gilberti, see Elliptocephala gilberti. 



howelli, see Elliptocephala howelli. 



iddingsi, see Elliptocephala iddingsi. 



vermontanus, Hall, 1859, see Mesonacis 



vermontana. 



OLENOIDES, Meek, 1877, Geol. Expl. 40th 

 Par., vol. 4, p. 25. [Ety. Olenus, and 

 oides form.] Ovate, head large, semi- 

 circular ; glabella straight or slightly 

 expanded in front; three pairs of fur- 

 rows ; eyes elongate; facial sutures ex- 

 tend obliquely outward from the an- 

 terior base of the eyes and cut the 

 frontal margin ; posteriorly they cut the 

 margin at the pleural angle, and run 

 subparallel to the margin to the pos- 

 terior end of the eye ; thorax with eight 

 or more segments ; axis strong, pleural 

 groove broad, and lobes well defined; 

 pygidium marked transversely on the 



