556 



CRUSTACEA. 



[MEN. MES. 



expanded anteriorly, no lateral fur- 

 rows, eyes large and close, posterior; 

 facial sutures 

 commencing 

 at the ante- 

 rior apex of 

 the shield, 

 curving lat- 

 erally, and 

 then con- 

 tracting to 

 the eyes in 

 front and 

 making a sig- 

 moidal flexure, cut the posterior mar- 

 gin midway between the dorsal furrows 

 and the genal spines ; pygidium sub- 

 triangular, outer margin bordered, and 

 terminating in a spine. Type M. 

 limbata. 



belemnura, White, 1874, Rep. Invert. 

 Foss., p. 11, and Geo. Sur. W. 100th 

 Mer., vol. 4, p. 59, Quebec Gr. or Up. 

 Taconic. 



FIG. 1030. Megalaspis belem- 

 nura. Pygidium. 



PiG. 1031. Mesonacis vermontana. 



MENOCEPHALUS, Owen, 1852, Geo. Sur. Wis., 

 Iowa, and Minn., p. 577. [Ety. mcnos, 

 strength; kephale, head.] Cephalic 

 shield semicircular, with a narrow bor- 

 der all around ; glabella highly con- 

 vex, hemispherical or ovate, with a 

 broadly rounded front, sometimes show- 

 ing two inconspicuous lateral furrows 



on each side ; cheeks tumid ; eyes dis- 

 tant from the middle of the ghibella ; 

 facial suture cuts the front margin a 

 little inside a line drawn lengthwise of 

 the body and through the eye, and cuts 

 the posterior margin a little outside 

 this line; thoracic segments six or 

 seven, axis convex, tapering a little 

 narrower than the side lobes ; pygidium 

 semicircular, axis and side lobes divided 

 by segmental furrows. Type M. min- 

 nesotensis. 



?globosus, Billings, 1860, Can. Nat. and 

 Geo., vol. 5, p. 301, and Pal. Foss., vol. 

 1, p. 408, Quebec Gr. or Up. Taconic. 



minnesotensis. Owen, 

 1852, Geo. 'Sur. Wis., 

 Iowa, and Minn., p. 

 577, Potsdam Gr. 



(?) salteri, Devine, 1863, 

 Can. Nat. and Geo., vol. 

 8, p. 210, and Pal Foss., 

 vol. 1, p. 203, Up. Ta- salteri. 



conic. 



?sedgwicki, Billings, 1860, Can. Nat. and 

 Geo., vol. 5, p. 301, and Pal. Foss., vol. 

 1, p. 407, Quebec Gr. or Up. Taconic. 

 MESONACIS, Walcott, 1885, Am. Jour. Sci. 

 and Arts, 3d ser., vol. 29, p. 328. [Ety. 

 meson, middle ; aids, point, spear.] 

 Head and first fourteen segments like 

 Elliptocephala, and the pygidium and 

 ten posterior segments like Paradox- 

 ides. Type M. vermontana. 



vermontana, Hall, 1859, (Olenus vermont- 

 anus,) 12th Rep. N. Y. St. Mus. Nat. 

 Hist., p. 60, Up. Taconic, Georgia Gr. 

 MESOTHYRA, Hall, 1888, Pal. N. Y., vol. 7, p. 

 Ivi. [Ety. mesos, middle ; thuris, small 

 door.] Carapace subquadrate; valves 

 in contact at the apices of two broad, 

 subtriangular extensions, situated on 

 the dorsal line opposite the eye nodes, 

 forming a broad and short anterior or 

 rostral cleft, and a long posterior cleft ; 

 test broadly infolded on the lower sur- 

 face, thickened and produced into a 

 conspicuous and acute posterior spine ; 

 posterior margin incurved and produced 

 into a short spine at the dorsal line ; 

 surface with a single strong carina on 

 each valve ; abdomen consisting of two 

 somites, of which the posterior is the 

 longer; post-abdomen with a broad 

 caudal plate, which is produced into a 

 relatively short telson ; lateral spines 

 long and setaceous. Type M. oceani. 



belli, Woodward, 1870, (Dithyrocaris 

 belli,) Geo. Mag., vol. 8, p. 106, Mid. 

 Devonian. 



neptuni, Hall, 1863, (Dithyrocaris nep- 

 tuni,) 16th Rep. N. Y. St. Mus. Nat. 

 Hist., p. 75, Ham. Gr. 



oceani, Hall, 1888, Pal. N. Y., vol. 7, p. 

 187, Portage Gr. 



spunuea, Hall, 1888, Pal. N. Y., vol. 7, p. 

 193, Ham. Gr. 



veneris, Hall, 1888, Pal. N. Y., vol. 7, p. 

 193, Ham. Gr. 



