REPORT OF THE STATE PALEONTOLOGIST 1902 



1087 



DISCUSSION OF SPECIES 

 Genus hughmilleria wn. 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 f i s c he r i, 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 en6$ 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 

 £i narrow doublure. Preoral appendages attached at the pos- 



