1818.] OF THE UNITED STATES. 433 



yellowish opposite spots on the disk, segments with the 

 hind edges whitish. 



Length half an inch. 



This species comes so near to the description of A. 

 maculatus that I should have considered it the same, had 

 it not been remarked that the maculatus is twice the 

 size of the vulgaris^ the former must therefore be much 

 larger than our species^ which is about equal in size to 

 the latter, as figured by Rcemer. It is very common in 

 moist places, under stones, in decaying wood, &c. 



Order V. BRANCHIOPODA. Latr. 

 Section I. PiECILOPA. Latr. 



Genus LIMULUS. Fabr. 



Head confounded with the thorax; antenna none; 

 mouth inferior, simple and central, surrounded by the 

 feei; mandibles and feet didactyle; cox^e supplying the 

 place of maxillae; tail elongated, attenuated. 



SPECIES. 



L. Polyphemus. Thorax scven-spined above; abdomen 

 above three-spined; tail about twenty- five-spined above; 

 feet^ second joint of the four anterior pairs, with about 

 five moveable spines. 



Monoculus Polyphemus of Linne. 

 Limulus Cyclops. Fabr. Syst. 

 Limulus polyphemus. Lam. 

 Polyphemus occidentalism Latr. 

 Limulus Sowerbii* Leach. Zool, Miscel. vol. ii* 

 pi, 84. Young. 



