TRILOBITES. 



123 



ing, that no Lrancliiopodous Entojnostraca has hitherto been 

 discovered capable of contracting itself into a ball, which 

 peculiai-ity is only observed in the isopodous genera Typhis, 

 Sphcsroma, Tylos, and Armadillo, figured above, and in the 

 apterous genus Glomeris, subsequently figured, between 

 which tribes there is a considerable hiatus. The genera Ca- 

 hjmene and Asaphus, amongst the Trilobites, on account of 

 their contractility, evidently approach the Glomeris and some 

 of the isopodous Crustacea {Spharoma) ; but the Trilobites 

 have the terminal segment of the body entire, and not fur- 

 nished with lateral swimmerets, as in the Sphceromce j the 

 same negative character however exists in the Glomeris, and 

 especially in the genus Tylos, of which the upper side of the 

 thoracic segments is divided into three lobes. The discovery 

 of the isopodous genus Serolis on the coasts of Patagonia has 

 afforded another proof of the correctness of Latreille's idea 

 of the osculant situation of these creatures between the 

 Isopoda and the mpiapodous insects, the eyes in that genus 

 being situated in the same vertical situation, and of the 

 same lunate form, as in the Trilobites. Moreover, the body 



Asaphus expansus. 



: rolled up. 



is longitudinally divided into three lobes, like the Trilobites. 

 The legs and caudal swimmerets scarcely extend beyond the 



