i8o 



HISTORICAL PALi^OXTOLOGY. 



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, w^hilst 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, PJiillipsia semhiifera, of the 

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

 of the natural size and enlarged — Coal-measures, Europe; c, Bivalved shell oi Entovio- 

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

 Scolder!, reduced in size — Mountain Limestone, Ireland ; e, Palceocaris typns, slightly 

 enlarged — Coal-measures, North America ; _/, AtithrapalcEinon gracilis, of the natural 

 size — Coal-measiires, 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 typiis (fig. 122, e) and the AntlwapalcRmon gracilis 

 (fig. i2 2,y), 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 " 



