t8o 



HISTORICAL PALEONTOLOGY. 



resemblance to the true Bivalve Molluscs (fig. 122,^). Lastly, 

 we meet for the first time in the Carboniferous rocks with the 

 remains of the highest of all the groups of Crustaceans name- 

 ly, the so-called " Decapods," in which there are five pairs of 

 walking-limbs, and the hinder end of the body (" abdomen ") 

 is composed of separate rings, whilst the anterior end is cov- 

 ered by a head-shield or " carapace." All the Carboniferous 

 Decapods hitherto discovered resemble the existing Lobsters, 



Fig. 122. Crustaceans of the Carboniferous Rocks, a, Ph>llips ; a setninifera, of the 

 natural size Mountain Limestone, Europe; b, One valve of the shell of Estheria tenella, 

 of the natural size and enlarged Coal-measures, Europe ; c, Bivalved shell of Entomo- 

 conchus Scouleri, of the natural size Mountain Limestone, Europe ; d, Dithyrocaris 

 Scouleri, reduced in size Mountain Limestone, Ireland ; e, Paleeocaris typus, slightly 

 enlarged Coal-measures, North America ; f, Anthrapalcemon gracilis, of the natural 

 size Coal-measures, North America. (After De Koninck, M'Coy, Rupert Jones, and 

 Meek and Worthen.) 



Prawns, and Shrimps (the Macrura], in having a long and well- 

 developed abdomen terminated by an expanded tail-fin. The 

 Palczocaris typus (fig. 122, e] and the Anthrapalcemon gracilis 

 (fig. 122, /), from the Coal-measures of Illinois, are two of the 

 best understood and most perfectly preserved of the few known 

 representatives of the " Long-tailed " Decapods in the Car- 

 boniferous series. The group of the Crabs or " Short-tailed " 



