80 



ARTICULATA. 



No. 136. [360, CastJ. Megachirus locusta, Germar. 



This Decapod from the Lithographic limestone (Middle Oolite), Solenhofen, 

 Bavaria, is the Locustrina marina of Bayer. It has a long tail, and a carapace 

 prolonged in front into a beak. But it is chiefly remarkable for the extreme 

 length of the anterior legs, which are clawless, and terminated with fin-like 

 appendages. Size, 9x5. 



ORDER MEROSTOMATA. 



Tlie Merostomata are a generalized type, with some resem- 

 blances to the Arachnoids and to the larvae of the Decapods. 

 They use for mastication the bases of the thoracic legs. The 

 sub-order Eurypterida appeared in the Upper Silurian and passed 

 out of existence with the Palaeozoic. They were the largest of 

 crustaceans, some being over six feet long. The King-crab 

 {Lirnulue) is the only living representative of the order. 



No. 137. [370, Cast]. Pterygotus acuminatus, Salter. 



This genus was established by Prof. Agassiz 

 in 1844. It derives its name from the pecu- 

 liar character of its foot-jaws, which, from 

 their scale-like sculpture, were at first mistaken 

 for the remains of a fish. Like the Eurypterus, 

 the Pterygotus maj^ be described as a "lobster- 

 like Crustacean," since it has an elongated body 

 composed of a cephalo-thorax, an abdomen with 

 a dozen segments, and a tail-plate. It differs 

 from the Eurypterus, in having a less number of 

 joints in the feet, in the eyes being marginal, and 

 in the large size of the antennae. This fine spec- 

 men was discovered in the Upper Silurian beds 

 of Leshmahago, Lanarkshire, Wales. 



Size, 24 X 13. 



No. 138. Eurypterus remipes, DeKay. 



The genus Eurypterus — the Idotea of Scouler — was established by DeKay 

 in 1825. The name is an allusion to the l)road, oar-like, swimming feet. The 

 body is composed of an anterior oval carapace, six thoracic and six abdom- 

 inal segments, and a somewhat obtuse tail-spine. The eyes were on the sur- 

 face of the carapace. There were five appendages, all oral, of which the 

 hinder pair were dilated into paddles. The basal joints of the first four legs 

 performed the work of mastication, as in the King-Crab. This specimen was 

 found in the Water-Lime Group (Upper Silurian), Buffalo, N. Y. 



