PALEOZOIC TIME — UPPEK SILUKIAN. 



i61 



816. 



Pentamerus limestone, and 810, 810 a, P. pseudo-galeatus, of the Upper Pen- 

 tamerus ; Pig. 814 is of Spirifer macropleurus, characteristic of the Shaly 

 limestone. Species of Spirifer and Orthis, and Gastropods of the genus 

 Platyceras were numerous. 



The Pentamerus (Anastrophia) Verneuili, Fig. 816, is a common species 

 in the Shaly limestone ; it occurs abundantly in the 

 Helderberg Mountains, and also in Schoharie, Car- 

 lisle, and other places. 



Orthocerata were few in species, of the genera 

 Orthoceras, Gomphoceras, Cyrtoceras, Oncoceras, and 

 others. A Gomphoceras, G. parvulum, of Whit- K/^j^^ 

 eaves. Fig. 817, occurs in beds of probably the lower 

 part of the series in Manitoba. Fig. 817 a shows 



the form of the aperture. PentamerusjAnastrophia) Ver- 



Among Trilobites occur species of Dalmanites, 

 Lichas, Acidaspis, Pliacops (Fig. 818), Bronteus (Fig. 819). Dalmanites pleu- 

 rop)teryx Green, D. nasutus Conrad, D. tridens Hall, having the front of the 

 head-shield at the center prolonged into a beak, and three-pointed ; Lichas 

 Bigsbyi Hall, L. pustulosus Hall, ornate with tubercles and having the margin 

 of the pygidium deeply dentate, are among the species. 



817. 



819. 



Cephalopod. — Fig. 81T, Gomphoceras parvulum ; 817 a, upper view showing aperture. Tkilobites. — Fig. 

 818, Phacops Loganl ; 819, Bronteus pompilius. 817, 817 a, Whiteaves ; 818, Hall ; 819, Billings. 



An upper view of the head of Acidaspis tuberculata is shown in Fig. 820, 

 a section of a segment of the thorax in 821, and the pygidium or caudal 

 extremity in 822. Fig. 824 is a dorsal view of the young of the same Tri- 

 lobite, when but a twenty-fifth of an inch long, as described by C. E. Beecher. 

 As the figure represents, the larve is nearly all head ; only a small lower 

 part of the figure corresponds to the posterior portion of the body. Fig. 825 

 shows the larval Acidaspis in profile. 



The genus Monticulipora and many others and a few Polyp-corals are described by 

 Hall in Pal. N. Y., vol. vi. ; Crinoids and Cystoids in Part vi., vol. iii. ; also Brachiopods, 

 Gastropods, Cephalopods, and Trilobites in the same ; Pteropods in vol. vii. 



DANA'S MANUAL — 36 



