1088 NEW YORK STATE MUSEUM 



terior end of the epistoma; short, stout, composed of three joints, 

 the two distal a little shorter than the basal, and forming a pair 

 of edentulous, bevel-edged pincers, which normally are folded 

 back so thatjtheir tips converge close to the anterior end of the 

 mouth. Endognathites increasing in length from the first back- 

 ward, moderately robust, spiniform, composed of seven joints, 

 of which the third to the sixth inclusive bear a pair of spines. 

 Swimming arms narrow, lanceolate paddles, composed of eight 

 joints and a rudimentary ninth inserted in a notch on the inner 

 side of the eighth or palette. The proximal joint, or gnathobase, 

 has the form of an upright retort. The seventh bears on the 

 inner half of the distal end a subtriangular lobe demarked by a 

 suture. Metastoma elongate, cordate. 

 Type, H. socialis Sarle. 



Comparison with other genera 



The characters suggesting Pterygotus are: the rounded tri- 

 angular or semielliptic outline of the head as seen in Pt. 

 b a n k s i i Salter (8) and Pt. raniceps Salter (8) ; the 

 marginal, compound eyes; the slender body with slight constric- 

 tion between the anterior and posterior abdominal portions; the 

 cordate form of the metastoma; and the simplicity of the opercu- 

 lar plate and its appendage. The two forms of this append- 

 age resemble those of Pterygotus as far as the material 

 of the latter permits of comparison, one form being a slender, 

 sagittate-based scale, the other a shorter, broader, convex body, 

 as in Pt. bilobus Salter (11) and Pt. osborni Hall 

 (10). In the new genus the first form projects posteriorly to 

 protect a shorter lance-linear appendage lying in a cleft of the 

 second sternite, while the second form is followed by an entire 

 sternite without appendage. The sixth pair of cephalothoracic 

 appendages resemble those of Pterygotus in being only slightly 

 expanded distally and consisting of eight joints, with a rudi- 

 mentary ninth inserted in the end of the palette. The gnatho- 

 bases have the upright retort form. 



This genus is distinguished most clearly from Pterygotus by 

 the character of the preoral appendages. These are stout, three- 



