i8o 



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, Phillipsia semitrfera, of the 

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

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

 C:icAus Sconlcri, of the natural size Mountain Limestone, Europe ; d, Dithyrocaris 

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

 enlarged Coal-measures, North America;^ Antlirapahemon gracills, 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 

 Palceocaris typus (fig. 122, e) and the Anthrapalcemon grarilis 

 (fig. 122, f), 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" 



