738 



THE WONDERS OF GEOLOGY. 



Lect. VII. 



which is a shell without septa, like that of the Argonaut : 

 and of the Orthoceras (Lign. 168, Jig. 12), which may 

 be described as a straight Nautilus, of an elongated, cylin- 

 drical shape, tapering to the extremity, and having entire 

 septa, pierced by a siphunculus (Jig. 13). The Orthoce- 

 ratites are often from twenty to thirty inches in circum- 

 ference at the largest extremity.* 



46. Crustaceans and Insects. — With the layers of 

 fresh-water shells that are intercalated in some of the 

 coal deposits, there are a few species of the fluviatile 

 crustaceans, the Cyjyrides, so abundant in the Wealden 

 and tertiary lacustrine limestones. Cyprides occur in 

 the Shrewsbury, and Burdie House strata, and in the 

 latter, two species of a branchiopodous crustacean (Eury- 

 pterus, Medals, p. 541,) one of which is twelve inches long, 

 have been discovered by Dr. Hibbert. 



In the ironstone nodules of 

 Coalbrook Dale, the remains 

 of small crustaceans sometimes 

 form the nucleus, and are in 

 a good state of preservation. 

 Some of these crustaceans are 

 referable to the Limulus, or 

 King-crab ; a genus which is 

 abundant in the seas of India 

 and America. The Limulus 

 has a distinct carapace or buck- 

 ler, and the last segment is 

 prolonged into a style ; it has 

 two eyes in front of the shield, and the gills are disposed on 

 lamelliform processes. A beautiful specimen of a fossil 

 Limulus from Coalbrook Dale is here figured (Lign. 169).f 



* Medals of Creation, p. 484. 



f The chemical changes which have taken place in the carboni- 

 ferous strata, and led to the formation of the hands and nodules of 



Lign. 1G9. — Limulus from Coal 



brook Dale. 



(Limulus trilobitoides.) 



