. POI,.] 



PISCES. 



607 



face punctate in undulate lines, but 

 without folds or ridges. Type P. lin- 

 eatus. 



lineatus, Newberry, 1875, Ohio Pal., vol. 



2, p. 58, Waverly Gr. 



PLATYSOMUS, Agassiz, 1833, Recherches sur 

 les Poissons Fossiles, t. 1, p. 6. [Ety. 

 platys, broad ; soma. body.] Rhom- 

 boidal, compressed; dorsal and anal 

 fins nearly equal, opposite ; pectorals 

 small ; yentrals small ; teeth clavate ; 

 crown dilated, flattened ; base slender, 

 constricted at the base of the ganoine; 

 scales large, oblong, articular internal 

 ridge at anterior edge ; beveled spine 

 at the upper corner received in a 

 notch of the adjoining scale. Type P. 

 striatus. 



circularis, Newberry & Worthen, 1870, 

 Geo. Sur. 111., vol. 4, p. 347, Coal 



Pleuracanthus, Agassiz, 1843, Poiss. Foss., 

 vol. 3, p. 66. [Ety. pleura, side ; akan- 

 tha, spine.] The genus was founded 

 upon a spine supposed to belong to the 

 Order Raiina. It is serrated on one 

 edge, curved at the base, and furrowed 

 on the inferior side. The species named 

 in this genus from America are too 

 poorly defined to warrant recognition. 

 Type P. Isevissimus. 



arcualus, see Orthacanthus arcuatus. 



biserialis, Newberry, 1857, Proc. Acad. 

 Nat. Sci., vol. 8, p. 100, Coal Meas. 



dilatatus, Newberry, 1857, Proc. Acad. Nat. 



Sci., vol. 8, p. 100, Coal Meas. 

 PNIGEACANTHUS, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 480. [Ety. from 

 the specific name in Oracanth us pnigeus; 

 akantha, spine.] Spine short, conical, 

 laterally compressed ; base broadly ex- 

 panded before and behind, without in- 

 sertion, rapidly tapering to the obtuse 

 apex, which is directed posteriorly ; 

 transverse section elliptical, rounded 

 into the slightly sigmoidally curved an- 

 terior border and concave posterior 

 margin ; pulp cavity very large, ex- 

 tending nearly to the tip ; lateral walls 

 very thin, slightly thickened in the 

 margins ; external surface occupied by 

 irregularly disposed, radiatingly sculp- 

 tured tubercles, sometimes arranged in 

 obscure or interrupted longitudinal and 

 diagonal order. The type is Oracan- 

 thus pnigeus, of Newberry & Worthen, 

 which St. John named Pnigeacanthus 

 deltoides. 



deltoides, St. John & Worthen, 1875, Geo. 

 Sur. 111., vol. 6, p. 480, Keokuk Gr. But 

 why should this species not be Pnigea- 

 canthus pnigeus? 



trigonal is, St. John & Worthen, 1883, Geo. 



Sur. 111., vol. 7, p. 259, St. Louis Gr. 

 POSCILODUS, Agassiz, 1843, Recherches Poiss. 

 Foss., vol. 3, p. 174. [Ety. poikilos, va- 

 riegated ; odous, tooth.] Teeth as in 

 Cpchliodus ; terminal tooth obliquely 

 trigonal, convoluted ; median tooth nar- 



row, convoluted; all teeth wrinkled at 

 right angles to the articular edges ; sur- 

 face porous. Type P. jonesi. 



carbonarius, St. John & Worthen, 1883, 

 Geo. Sur. 111., vol. 7, p. 139, Coal 

 Meas. 



cestriensis, St. John & Worthen, 1883, 

 Geo. Sur. 111., vol. 7, p. 135, Kaskas- 

 kia Gr. 



ornatus, Newberry & Worthen, 1866, Geo. 

 Sur. 111., vol. 2, p. 95, syn. for Chitono- 

 dus rugosus. 



rugosus, see Chitonodus rugosus. 



springeri, St. John & Worthen, 1883, Geo. 

 Sur. 111., vol. 7, p. 138, Subcarbon- 

 iferous. 



stludovici, St. John & Worthen, 1883, 

 Geo. Sur. 111., vol. 7, p. 132, St. 

 Louis Gr. 



varsoviensis, St. John & Worthen, 1883, 

 Geo. Sur. 111., vol. 7, p. 131. War- 

 saw Gr. 



wortheni, St. John, 1883, Geo. Sur. 111., 



vol. 7, p. 136, Kaskaskia Gr. 

 POLYRHIZODUS, McCoy, 1848, Ann. and Mag. 

 Nat. Hist, 2d series, vol. 2, p. 125. 

 [Ety. polys, many ; rhiza, root ; odous, 

 tooth.] Crown like Petalodus, but 

 more elongated, transversely lower and 

 thicker; root divided into numerous 

 short, robust radicles. Type P. 

 magnus. 



amplus, St. John & Worthen, 1875, Geo. 

 Sur. 111., vol. 6, p. 387, St. Louis Gr. 



carbonarius, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 389, Coal 

 Meas. 



dentatus, Newberry & Worthen, 1866, 

 Geo. Sur. 111., vol. 2, p. 50, . Kaskas- 

 kia Gr. 



littoni, Newberry & Worthen, 1870, Geo. 

 Sur. 111., vol. 

 4, p. 357, St. 

 Louis Gr. 



modestus, New- 

 berry, 1875, 

 Ohio Pal., vol. 

 9 r> s;n Plovo- Fl - 1160. Poly rhizodus lit- 



land shale ton1 ' <*<"* 



nanus, St. John & Worthen, 1875, Geo. 

 Sur. 111., vol. 6, p. 

 386, Keokuk Gr. 

 piasensis, St. John & 

 Worthen, 1875, 

 Geo. Sur. 111., vol. 

 6, p. 386, Warsaw 

 Gr. 



ponticulus, Newberry & Worthen, 1866, 

 Geo. Sur. 111., vol. 2, p. 51, Kaskas- 

 kia Gr. 



porosus, Newberry & Worthen, 1866, 

 Geo. Sur. 111., vol. 2, p. 49, Burling- 

 ton Gr. 



truncatus, Newberry & Worthen, 1870, 

 Geo. Sur. 111., vol. 4, p. 357, Burling- 

 ton Gr. 



williamsi, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 384, Keo- 

 kuk Gr. 



?:> 



FIG. 1161.-Polyrhlzo- 

 dus modestus. 



