180 HISTORICAL PALAZZONTOLOGY. 
resemblance to the true Bivalve Molluscs (fig. 122,4). 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, 
oT () E a 
5G, oS, 
Fig. 122.—Crustaceans of the Carboniferous Rocks. a, Phillipsia sentinifera, of the 
natural size—Mountain Limestone, Europe; 4, One valve of the shell of Estheria tenella, 
of the natural size and enlarged—Coal-measures, Europe; c, Bivalved shell of Z7¢omz0- 
conchus Scouleri, of the natural size—Mountain Limestone, Europe; d, Dithyrocaris 
Scoulerz, reduced in size—Mountain Limestone, Ireland ; e, Paleocaris typus, slightly 
enlarged—Coal-measures, North America; 4, Anthrapalemon gracilis, of the natural 
size—Coal-measures, North America. (After De Koninck, M‘Coy, Rupert Jones, and 
Meek and Worthen.) 
Prawns, and Shrimps (the JZacrura), in having a long and well- 
developed abdomen terminated by an expanded tail-fin. The 
"uleocaris typus (fig. 122, e) and the Anthrapalemon gracilis 
(fig. 122, 7), 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” 
