398 NORTH AMERICAN INDEX FOSSILS. 



XXVIII. AcANTHOTELSON Meek and Worthen. 

 Elongate, slender Crustacea with many-ringed body, the rings 

 of the thorax and abdomen of about the same length; head about 

 the length of two thoracic segments ; antennae of equal length, the 

 inner pair biramous, flagella longer than peduncle ; anterior tho- 

 racic legs longer than others; telson long, simple, spine-like, lat- 

 erally compressed; stylets with second segment longer than first 

 and similar to telson, and all setigerous. Carbonic. 



Fig. 1696. Acanthotehon stimpsoni : a, dorsal view ; 3, side view ; r, anterior portion 

 enlarged, showing antennse and anterior thoracic legs ; a', stylet enlarged. (Ind. Surv. ) 



48. A. Stimpsoni Meek and Worthen. (Fig. 1696.) Carbonic. 

 Both pairs of antennae very long; 14 thoracic and abdominal 



segments. (Type of genus.) 

 Coal Measures of Illinois. 



Order ISOPODA Latreille. 



Vertically flattened, elongate Crustacea, inhabiting salt and more 

 rarely fresh water, while a number of them are terrestrial; body 

 flat below, rounded above ; seven free thoracic segments ; carapace 

 scarcely developed ; abdomen of short, ringed and often reduced, 

 partially fused segments ; caudal segment comparatively large and 

 shield-shaped. 



XXIX. Amphipeltis Salter. 



Carapace oblong, oval, rounded anteriorly, truncated behind ; 

 thorax with nine segments, five of which project behind the cara- 

 pace, while four are concealed beneath it ; caudal segment semi- 

 circular, of same width as abdomen and equal in length to the 

 last three segments. 



49. A. paradoxus Salter. Devonic? or Carbonic. 

 Length of carapace fully three fourths of an inch ; breadth some- 

 what less; surface without ornamentation; margins minutely ser- ^ 



