392 



ARTHROPODA. 



Fig. 247. Anthrapalcemon graeilis, 

 of the natural size. From the Coal- 

 measures of North America. (After 

 Meek and Worthen.) 



gracilis of the Coal-measures of Illinois (fig. 247). In this 

 species, as in all belonging to the genus, there is a well- 

 developed carapace, which is fur- 

 nished with a beak or " rostrum " 

 in front, and, typically, with ser- 

 rated lateral margins. There are 

 five pairs of thoracic legs; the 

 abdomen is composed of free seg- 

 ments ; and there is a caudal fin, 

 formed by the telson along with 

 the last pair of " swimmerets." 

 The genus Anthrapalcemon is not 

 allied, as its name would seem to 

 imply, to the true Prawns (Palce- 

 mori), but seems to be rather re- 

 lated to the living GalatJiea. 



In the Permian rocks no un- 

 doubted remains of Macrura have 

 been as yet detected. In the 



Trias, however, we meet with examples of the genera Gala- 

 tJiea and Litogaster, along with others of less importance. 

 In the Jurassic and Cretaceous strata " Long-tailed " De- 

 capods are extremely abundant, and are often beautifully 

 preserved. Amongst the more remarkable of the Jurassic 

 genera may be mentioned Eryon (fig. 248), which com- 

 mences in the Lias, but attains its maximum in the 

 Middle Oolitic strata, being especially abundant in the 

 fine-grained Lithographic Slates of Solenhofen. In this 

 singular genus the carapace is large and broad, and nearly 

 quadrate in figure, whilst the antennae are very small. The 

 genus is nearly allied to the living Willemoesia. Another 

 singular genus from the Solenhofen Slates is Mecochirus (or 

 Megachirus), in which the first pair of legs is enormously 

 elongated, but not terminated by chelae. Von Seebach has 

 also shown that the same deposits contain the remains of 

 " Phyllosomse," which may be regarded as the larval forms of 

 such Palinuroid genera as Eryon. In the Cretaceous rocks 

 are numerous Macrourans, belonging to the genera Meyeria, 

 Enoplodytia, Hoploparia, &c. In many parts of the Tertiary 



