PER. PIS.] 



ECHINODERMA TA. 



269 



plates imbricating upward, and from 

 the center outward ; primary spines on 

 the rows adjoining the ambulacra, the 

 supporting tubercle being small, per- 

 forated, but not crenulated, and sur- 

 rounded by a double ring; ovarian 

 plates having 6 pores ; mouth and anal 

 openings small, central. Type P. 

 biserialis. 



illinoisensis, Worthen & Miller, 1883, 

 Geo. Sur. 111., vol. 7, p. 333, Kas- 

 kaskia Gr. 



PereiocJiocrinus, Austin, 1843, Ann. and 

 Mag. Nat. Hist., vol. 11, p. 203. Not 

 defined so as to be recognized, though 

 some authors use it instead of Sacco- 

 crinus. 



PETRASTER, Billings, 1858, Can. Org. Rem., 

 Decade 3, p. 79. [Ety. petros, stone ; 

 aster, star.] Closely related to Palseas- 

 ter, and having both marginal and 

 adambulacral plates, with a few disk- 

 plates, on the ventral side. Type P. 

 rigidus. 



FIG. 389. Pet nister bellulus. 



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

 p. 393, Niagara Gr. 



rigidus, Billings, 1857, (Palseasterina rig- 

 idus,) Rep. of Progr. Geo. Sur. Can., p. 

 291, and Can. Org. Rem., Decade 3, p. 

 80, Trenton Gr. 



wilberianus, see Palaeaster wilberanus. 

 Philocrinus, Koninck, 1863. [Ety. phihs, 

 favorite ; krinon, lily.] 



pelvis, Meek & Worthen, 1865, Am. Jour. 

 Sci., 2d series, vol. 39, syn. for Eriso- 

 crinus typus. 



PHOLIDOCIDARIS, Meek & Worthen, 1869, 

 Proc. Acad. Nat. Sci. Phil., p. 77. [Ety. 

 pholidos, scale ; kideris, turban.] Inter- 

 ambulacrals thin, irregular, imbricating 

 upward and laterally ; five or more 

 rows ; only two reaching the extremi- 

 ties ; marginal rows and those on the 

 lower side having primary tubercles, 

 showing a pit in the top, and being 

 surrounded by two rings; ambulacral 

 areas wide, with six or more rows of 

 plates imbricating downward, each 

 plate pierced by two pores, and the 

 larger ones having additional pores. 

 Type P. irregularis. 



irregularis, M^-k & Worthen, 1869, Proc. 

 Acad. Nat. Sci. Phil., p. 78, and Geo. 

 Sur. 111., vol. 5, p. 512, Keokuk Gr. 



PHYSETOCRINUS, Meek & Wortheu, 1869, 

 Proc. Acad. Nat. Sci. Phil., p. 158. 

 [Ety. physetos, inflated ; krinon, lily.] 

 Distinguished from Actinocrinus, in 

 the form and construction of the vault, 

 which has no proboscis, and has pores 

 along the radial portions of the dome; 

 and, also, in having no hook-like pro- 

 jections along the pinnules. Type P. 

 ventricosus. 



asper, Met-k & Worthen, 1869, Proc. 

 Acad. Nat. Sci. Phil., p. 161, and Geo. 

 Sur. 111., vol. 5, p. 351, Burlington Gr. 



copei, S. A. 

 Miller, 1881, 

 (Actinocrinus 

 copei,) Jour. 

 Gin. Soc. Nat. 

 Hist., vol. 4, p. 

 310, Burling- 

 ton Gr. 



dilatatus, Meek 

 & Wor then, 

 1869, (Stroto- FlQ 3 9o._p tl ysetocrina8 

 crinus dilata- copei. 



tus , ) Proc . 



Acad. Nat. Sci. Phil. p. 162, and Geo. 

 Sur. 111., vol. 5, p. 363, Burlington Gr. 



ornatus, Hall, 1858, (Actinocrinus or- 

 natus,) Geo. Sur. Iowa, p. 583, Burling- 

 ton Gr. 



reticulatus, Hall, 1861, (Actinocrinus 

 reticulatus ) Desc. New Crin., p. 3, 

 Burlington Gr. 



subventricosus, McChesney, 1860, (Acti- 

 nocrinus subventricosus,) Desc. New 

 Crin. Pal. Foss., p. 21, and Trans. Chi. 

 Acad. Sci.,* p. 16, Burlington Gr. 



ventricosus, Hall, 1858, (Actinocrinus 

 ventricosus,) Geo. Sur. Iowa, p. 595, 

 Burlington Gr. 



ventricosue var. cancellatus, Hall, 1861, 

 (Actinocrinus ventricosus var. cancel- 

 latus,) Bost. Jour. Nat. Hist., vol. 7, p. 

 279, Burlington Gr. 



ventricosus var. internodus, Hall, 1861, 

 (Actinocrinus ventricosus var. inter- 

 nodus,) Bost. Jour. Nat. Hist., vol. J, 

 p. 278, Burlington Gr. 



PISOCRINUS, DeKoninck, 1858, Bull. Acad. 

 Roy. Belgique, 2me ser., tome 3, p. 24. 

 [Ety. pisos, pea; krinon, lily.] Calyx 

 round globular; basals 5, forming a 

 triangle; these are followed by three 

 large plates, forming nearly the entire 

 calyx; one of these supports two small 

 plates, and a small plate is supported, 

 in a notch, between the other two 

 larger plates; arms 5; column round. 

 Type P. pilula. ; 



gemmiformis, S. A. Miller, 

 1879, Jour. Gin. Soc. 



FiG.39i.-pisocH- HfJKSj x K 2 ' p - 



nus gemmifor- ", JSiagara Gr. 

 mis. Natural globosus, Ringueberg, 

 1884, (Triacrinus glob- 

 osus,) Proc. Acad. Nat. 

 Sci. Phil., p. 146, Clinton Gr. 



size and magni- 

 fied. 



