ACERATA—MEROSTOMATA. 



413 



In the dark shales of the Shawangunk conglomerate (Lower 

 Salina) of eastern New York and Pennsylvania ( ?). 



28. H. socialis Sarle. (Fig. 1714.) Siluric. 



Telson comparatively long and pointed; surface of entire speci- 

 men covered with imbricating, crescentic or angular scales, some- 

 times carrying smaller ones of same pattern. (Type of genus.) 



Pittsford shales (Lower Salina) of New York. 



Fig. 1 7 13. a-c, Hughmilleria shawangunk; a, nearly entire, 40 mm. long; b^ 

 average mature individual, X 3 5 '^» youngest individual, 2.5 mm. long ; d^ e, Euryp- 

 terus maria, X | and X 2 ; /, ^, E. myops, head shields, X ' and X f- (After 

 Clarke. ) 



XV. Stylonurus Page. 

 Body similar in general proportions to Pterygotus, and often 

 exceeding three feet in length; cephalothorax quadrate or five- 

 sided, its margins bent under so as to cover more than one half 

 of the ventral surface; eyes large, close together, sometimes sur- 

 rounded by strong ridges; ocelli on the slope of a median ridge; 

 appendages from before the mouth known only by fragments of 

 small chelae. Of the five pairs of appendages behind the mouth 

 the first bears chelae, the next two are short and each joint bears 

 a pair of lamellar processes; the last two pairs are enormously 

 elongated, nine-jointed, extending almost to the end of the telson 

 and terminating in sharp claws; number of abdominal segments 

 probably the same as in Eurypterus; telson long and slender. 

 Siluric and Devonic. 



