412 NORTH AMERICAN INDEX FOSSILS. 



26. A. mazonensis Meek and Worthen. (Fig. 1712.) Carbonic. 



Large, abdomen abruptly contracted after the fifth segment; 

 cephalothorax semioval. (Type of genus.) 



Coal Measures of Mazon Creek, Illinois. 



Fig. 1 7 12. Anthraconectes mazonensis, an outline of the ventral side, X Yi- 



a, b, c, crushed and broken legs, as they appear in the specimens ; the divisions 

 shown are not all natural articulations, gg, basal segments of the swimming feet. 

 h, h, h, h, hy impressions of the angular ends of the dorsal half of the body segments. 

 m^ hypostoma, in place. M, mesial appendage of the operculum; i, 2, 3, are its 

 apparent articulations ; x, x, and /, /, are lateral alse of the operculum. 0, position of 

 the mouth, p, one of the paddles or swimming feet, imperfect. The division at i 

 seems to be a natural joint. 



b, hypostoma enlarged, to show surface sculpturing. 



c, a portion of basal segment of swimming-foot enlarged to show surface sculpturing. 



XIV. HuGHMiLLERiA Sarlc. 

 Cephalon rounded, triangular, or elliptical, with marginal com- 

 pound eyes ; body slender with slight constriction ; appendages 

 similar to Pterygotus; preoral appendages stout, three-jointed and 

 chelate, barely half the length of cephalothoracic shield when ex- 

 tended; pincers edentulous; spiniform walking legs of seven joints, 

 proportionally more robust than in Pterygotus, and each joint 

 from third to sixth, inclusive, carries a pair of ventrally and dis- 

 tantly articulated, slender curved spines ; abdomen without marked 

 contraction, of twelve segments exclusive of telson. Siluric. 



27. H. shawangunk Clarke. (Figs. 1713,0-^; 1705,^, ^.) Siluric. 

 Similar to H. socialis but much smaller ; the young with abrupt 

 constrictions after fifth abdominal segment; telson broad, stouter 

 and more triangular than in type. 



