REPORT OF THE STATE PALEONTOLOGIST 1902 1087 



DISCUSSION OF SPECIES 

 Genus hughmilleria gen. no v. • 

 By far the most abundant of the eurypterids occurring in this 

 stratum of black shale near the base of the Salina, is a small 

 form which, from its general appearance, in many ways suggests 

 the genus Eurypterus, while a study of its structure shows it 

 to be closely related to Pterygotus. It is evidently a new genus, 

 which it is proposed to designate by the name Hughmilleria. 



Generic diagnosis 

 General outline lanceolate. Cephalothorax semielliptic and 

 flatly convex; compound eyes small, subelliptic and marginal; 

 ocelli subcentral. Abdomen divided into distinct anterior and 

 posterior regions. Preabdomen provided dorsally with six 

 plain, transverse, bandlike tergites; ventrally with five stern- 

 ites, the last three being essentially like the corresponding dor- 

 sal plates. First sternite cleft for the reception of a median 

 appendage, which varies in form according to sex. Basing 

 sexual distinctions on the determinations made by Holm in 

 Eurypterus fischeri, this appendage in the female 

 consists of a narrow, convex, scalelike, sagittate-based sheath, 

 which appears to be formed by the fusion of two nearly 

 equal portions, the anterior overlapping, and projecting poster- 

 iorly to cover partially a slightly shorter, simple, lance-linear ap- 

 pendage in a cleft of the following sternite. In the male the 

 appendage is confined to the first sternite, the second being en- 

 tire. It is proportionately shorter and broader, convex and 

 lanceolate with the posterior free end slightly produced. Post- 

 abdomen composed of six ring segments. The first is readily 

 distinguished from the segments of the preabdomen by post- 

 lateral prolongations. It appears to be formed by the fusion 

 at their appressed ends, of a sternal and a tergal portion, the 

 latter of which is the longer. The following segments are sim- 

 ple, bandlike rings. Telson long, lanceolate, with dorsal carina- 

 tion. Epistoma convex, peltiform, dividing in molting or under 

 stress of compression, through the middle, joined at the sides to 

 a narrow doublure. Preoral appendages attached at the pos- 



