Explanation of Fig. 187. — Crinoidea: a, Eucalyptocrinus crassus Hall, a complete cri- 

 noid, showing root, stem, and body; b, Callicrinus murchisonianus Ang., showing 

 extraordinary spinose ornamentation; c, Petalocrinus mirabilis \V eller, showing a 

 remarkable type of arm differentiation, the arms being consolidated into five tri- 

 angular plate-like bodies; d, Lecanocrinus macro petalus Hall, one of the articulate 

 crinoids; e, Crotalocrinus pulcher (His.), a crinoid with remarkably differentiated 

 arms. Cystoidea: f, Caryocrinus ornatus Say., a cystoid with regularly arranged 

 body-plates ; the pores may be seen arranged in radiating lines from the centres of 

 the plates ; g, Callicystis jewetti Hall, a cystoid with unsymmetrical arrangement of 

 plates, the arm furrows recumbent, the pores arranged in groups; h, Holocystites 

 adiapatus Miller, a cystoid with irregularly arranged plates and scattered pores. 

 Blastoidea: i, Troostocrinus reinwardtii (Troost), showing the typical bud-shaped 

 form of these organisms. Spongs: j, Astrceospongia meniscus Koem., a saucer- 

 shaped sponge with exceptionally large spicules; k, Astylospongia prcemorsa 

 (Goldf.), a globular sponge showing the osculum above and the ends of the water 

 canals. Cephalopoda: I, Orthoceras annidatum Sow., a straight chambered 

 shell with annulations; m-n, Phragmoceras nestor Hall, lateral and end views of 

 a curved chambered shell with peculiar constricted aperture. Brachiopoda: 

 o, Pentamerus oblongus Murch., lateral view of an internal cast; p, Spirifer niaga- 

 rensis (Con.), exterior view of the brachial or dorsal valve, with the cardinal area 

 and beak of the pedicle or ventral valve showing above; q, Spirifer radiatus Sow., 

 a view similar to the last. These two figures show the plicated and non-plicated 

 spirifer shells, marked with fine radiating striae; r, Trimerella ohioensis Meek, 

 the internal cast of a highly differentiated inarticulate brachiopod, showing the 

 finger-like casts of the excavations beneath the elevated muscular platforms; 

 s, Trimerella acuminata Bill., the interior view of a pedicle or ventral valve, show- 

 ing the elevated platform for muscular attachment, excavated beneath; t, u, 

 Stropheodonta profunda Hall, interior of the pedicle or ventral valve, snowing 

 muscular impressions, cardinal area, delthyrium, and crenulated hinge line, 

 with an enlarged view of the area and hinge; v, Chonetes cornutus (Hall), exterior 

 view of pedicle or ventral valve, showing the cardinal spines; w, Streptis grayi 

 (Dav.), exterior view of the brachial or dorsal valve, showing the cardinal area 

 and beak of the opposite valve and the peculiar twisted form of the shell; x, 

 Rhynchotreta cuneata (Dal.), exterior view of the brachial or dorsal valve, showing 

 the beak and pedicle opening of the opposite valve. Trilobita: y, Sphcerexochus 

 mirus Bey., dorsal view; z, Staurocephalus murchisoni Barr, dorsal view, showing 

 the peculiar globular anterior prolongation of the head; tt, Deiphon forbesi Barr, 

 dorsal view of a peculiar trilobite having the pleural lobes much reduced; uu, 

 Calymene niagarensis Hall, dorsal view of one of the commonest Silurian trilo- 

 bites ; vv, Cyphaspis christyi Hall, dorsal view. Pelecypoda: ww, Pterinea emacerata 

 (Con.), exterior view of the left valve. Gastropoda: xx, Loxonema leda Hall; 

 yy, Subulites ventricosus Hall; zz, Platyostoma niagarensis Hall, views of three types 

 of Silurian coiled shells. (Weller.) 



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