564 



CRUSTACEA. 



[PTE. — PTY. 



slight curvature, to just within the 

 cheek spine ; thorax, twelve segmeuts, 

 strongly trilobed ; pleura straight, 

 broadly channeled and pointed; pygid- 

 ium small, semielliptical, and marked 

 by three furrows on the small axis and 

 lateral areas. Type P. hitchcocki. 



hitchcocki, Whitfield, 1884, (Angelina 

 hitchcocki,) Bull. Am. Mus. Nat. Hist., 

 vol. 1, p. 148, Up. Taconic. 

 Ptebocephalia, Roemer, 1849, Texas, mit 

 naturwissench. Aahang. Bonn., and 

 afterward in 1852, Kreid von Texas, p. 

 92. [Ety. pteron, wing; kephale, head.] 

 Cephalic shield semicircular, nearly 

 flat; glabella less than half the length 

 of the head shield, with a flat, wing- 

 like projection in front; two or three 

 furrows on each side; neck furrow dis- 

 tinct ; facial sutures din cted nearly 

 straight back from the anterior margin 

 to the eye, after passing which it is di- 

 rected at an angle laterally of about 

 forty- five degrees to the posterior mar- 

 gin ; eyes situate nearly opposite the 

 posterior lobe of the glabella; pygid- 

 ium subcircular, margin flattened and 

 produced ; axial lobe narrow, about ten 

 segments. Type P. sanctisah.-e. 



laticeps, Hall & Whitfield, 1877, (Cono- 

 cephalites laticeps,) Geo. Ex pi. 40th 

 Par., vol. 4, p. 221, Potsdam. Gr. 



occidens, Walcott, 1884, Mon. U. S. Geo. 

 Sur., vol. 8, p. 58, Potsdam Gr. 



sanctisabae, Roemer, 1849, Texas, mit 

 naturwissench. Anhang., and in 1852, 

 Kreid von Texas, p. 92, Potsdam Gr. 

 Pterygotus, Agassiz, 1839, March. Sil. Syst, 



6, 605. [Ety. pteron, wing ; out, ear.] 

 istinguished from Eurypterus by hav- 

 ing eyes marginal instead of within the 



Fig. 1051.— Pterygotus problematlcus. 



carapace, twelve segments instead of 

 thirteen in the body, a bilobate caudal 

 extremity and chelate antennae at the 

 anterior part of the carapace. Type P. 

 problematicus. 



acuticaudatus, Pohlman, 1882, Bull. Buf. 

 Soc. Nat. Sci., vol. 4, p. 42, Waterlime Gr. 



buffaloensis, Pohlman, Bull. Buf. Soc. 

 Nat. Hist., vol. 4, p. 17, Waterlime Gr. 



cobbi, Hall, 1859, Pal. N. Y., vol. 3, p. 417, 

 Waterlime Gr. 



cummingsi, Grote & Pitt, 1875, Bull. Buf. 

 Soc.'lSat. Hist., vol. 4, p. 18, Water- 

 lime Gr. 



globicaudatus, Pohlman, 1882, Bull. Buf. 

 Soc. Nat. Hist., vol. 4, p. 42, Water- 

 lime Gr. 



macrophthalmus, Hall, 1859, Pal. N. Y., 

 vol. 3, p. 418, Waterlime Gr. 



osborni, Hall, 1859, Pal. N. Y., vol. 3, p. 

 419, Waterlime Gr. 



quadraticaudatus, Pohlman, 1882, Bull. 

 Buf. Soc. Nat. Hist., vol. 4, p. 43, Water- 

 lime Gr. 

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

 Mus. Nat. Hist., p. 170. [Ety. ptyche, 

 fold ; aspis, shield.] Cephalic shield 

 broad, with wide depressed convex 

 cheeks; glabella cylindrical, convex, 

 transversely lobed, prominent in front; 

 eyes anterior to the middle ; facial suture 

 cutting the anterior border almost in 

 front of the eye, and from below the 

 eye it proceeds obliquely to the base a 

 little without the center of the cheek, 

 leaving the movable cheek near the size 

 of the fixed cheek; movable cheek sub- 

 trapezoidal, border thickened, and ex- 

 tended backward in a spine. Type P. 

 miniscensis. 



barabuensis, Winchell, 1864, Am. Jour. 

 Sci. and Arts, 2d ser., vol. 37, p. 230, 

 Potsdam Gr. 



granuloma, Owen, 1852, (Dikelocephalus 

 granulosus) Geo.Wis., Iowa, and Minn., 

 p. 575, Potsdam Gr. 



miniscensis, Owen, 1852, (Dikelocephalus 

 miniscaensis,) Geo. Wis., Iowa, and 

 Minn., p. 574, Potsdam Gr. 



minuta, Whitfield, 1878, Ann. Rep. Geo. 

 Snr. Wis., p. 55, and Geo. of Wis., vol. 

 4, p. 186, Potsdam Gr. 



pustulosa, Hall & Whitfield, 1877, U. S. 

 Geo. Expl. 40th Par., vol. 4, p. 223, 

 Potsdam Gr. 



sesostris, Billings, 1865 

 (Dikelocephalus se- 

 sostris), Pal. Foss., 

 vol. 1, p. 198, Quebec 

 Gr. or Up. Taconic. 



speciosa, Walcott, 1879, 



32d Rep. N. Y. St. Fig. 1052.-Ptychaspis 

 Mus. Nat. Hist., p. sesobtrls. 



131, Calciferous Gr. 



striata, Whitfield, 1878, Ann. Rep. Geo. 

 Sur. Wis., p. 55, Potsdam Gr. 

 Ptychoparia, Corda, 1847, Prodrom. einer 

 Monographie der bohmischen Trilo- 

 biten, p. 141. [Ety. ptyche, fold.] Ce- 

 phalic shield semilunar ; genal angle 

 spined or pointed ; glabella narrow an- 

 teriorly, elevated ; furrows four, distinct, 

 directed forward ; facial sutures widely 

 separated, extending and converging 



