606 



HISTORICAL GEOLOGY. 



obtained in the beds of Cmcinnati of the Hudson period, and in part differ 

 somewhat in habit from those of the Trenton limestone. 



652-655. 



652. 







Beyozoans. — Fig. 652, Stictoporella cribrosa (1) ; 653, same 

 (x 18) ; 654, Arthroclema Billingsi (1) ; 655, A. cornutum 

 (X 7). Ulricli. 



6. Mollusks. — Some of the Lamelli- 

 branchs are figured in Nos. 670-672, and 

 also 709-712 (page 511) ; and Gastropods in 

 Figs. 673-681. Fig. 673 represents a Ba- 

 phistoma ; 674, 675, species of the genus 

 Murcliisonia; 677, 678, a Belleroplion in 

 different views ; and 679-681, species of 

 the related genus Cyrtolites, symmetrical 

 shells of swimming Mollusks, related to 

 the modern Atlantis (Heteropods). 



Pteropods were represented by species 

 of Pterotlieca, and of Conularia; in the 

 latter, the shell admits of some movement along vertical sutures (Fig. 682). 



A few of the shells of Cephalopods are represented on page 508 : Fig. 

 683, Orthoceras junceum H. ; the cross-lines representing the partitions or 

 septa, and Fig. a, a transverse section, showing the position and size of 

 the siphuncle. Fig. 685, part of the shell of Actinoceras Bigshyi of Bronn 

 (1837); the whole length of the shell when entire was over a foot; the 

 view is of a section showing the large beaded siphuncle within ; 686, Cyrto- 

 ceras subannulatum D'Orb. ; and 687, 688, species of TrochoUtes, T. undatus 

 and T. Ammonius of Conrad. In another genus, Endoceras, from the Black 

 River limestone, some specimens have a diameter exceeding a foot, and a 



