Oil. XXIV.] 



ckustaceatn^s of the coal. 



385 



Fig. 500. 



In the lower coal-measures of Coalbrook Dale, the strata, accord- 

 ing to Mr. Pi'estwich, often change completely within very short dis- 

 tances, beds of sandstone passing horizontally into clay, and clay intc 

 sandstone. The coal-seams often wedge out or disappear ; and sections, 

 at places nearly contiguous, present marked lithological distinctions. 

 In this single field, in which the strata are from 700 to 800 feet thick, 

 between forty and fifty species of terrestrial plants have been discovered, 

 besides several fishes of the genera Megalichthys^ Holoptychius, and 

 others. Crustacea also are met with, of the 

 genus Limalus (see fig. 500), resembling in 

 all essential characters the Limuli of the 

 Oolitic period, and the king-crab of the 

 modern seas. They were smaller, howevei-, 

 than the living form, and had the abdomen 

 deeply grooved across, and serrated at its 

 edges. In this specimen, the tail is wanting ; 

 but in another, of a second species, from 

 Coalbrook Dale, the tail is seen to agree with 

 that of the living Limulus. 



The perfect carapace of a long-tailed or decapod crustacean has 

 also been found in the iron-stone of these strata by Mr. Ick (see fig. 

 501). It is referred by Mr. Salter to Olypliea^ a genus also occur- 

 ring in the Lias and Oohte. There are also 

 upwards of forty species of mollusca, among 

 which are two or three referred to the fresh- 

 water genus Unio^ and others of marine 

 forms, such as Nautilus^ Orthoceras, Spirifer, 

 and Productus. Mr. Prestwich suggests that 

 the intermixture of beds containing freshwater 

 shells with others full of marine remains, 

 and the alternation of coarse sandstone and 

 conglomerate with beds of fine clay or shale 

 containing the remains of plants, may be ex- ^^^^^^^^ , ^^^^^.^^ g^,^^^_ 

 plained by supposing* the deposit of Coalbrook Syn. Apus duUus, Miine Edward?. 



1^,, ..-. , „, The oldest recorded decapod (or 



Dale to have originated m a bay ot the sea or long-taiied) crustacean. Coai- 



, •, I'lij 1 -J IT* measures, Coalbrook Dale. 



estuary into which flowed a considerable river 

 subject to occasional freshes.* 



One or more species of scorpions, two beetles of the family Curcu- 

 lionidce, and a neuropterous insect resembling the genus Corydalis, and 

 another related to the Fhasmidce, have been found at Coalbrook Dale. 

 From the Coal of Wetting in Westphalia several specimens of the cock- 

 roach or Blatta family, and the wing of a cricket [Acridites), have been 

 described by Germar.f 



Zimuhis 7'otundatus, Prestwich. 

 Coal, Coaibrook. Dale. 



Fig. 501. 



* Prestwich, Geol. Trans., 2d series, vol. v. p. 440. 

 f See Munster's Beitr. vol. v. pi. 13, 1842. 

 25 



