Page:The Eurypterida of New York Volume 1.pdf/335

 segments of the endognathite, the peculiar character of the scales and the longitudinal ridges of the segment.

The multispinosity of the segments is a notable character of the genera Stylonurus and Dolichopterus and of a few rather aberrant species of Eurypterus and Eusarcus. The arrangement of the spines in Megalograptus is rather bunched and in this regard differs from the prevailing serial arrangement in Stylonurus and Dolichopterus, and resembles more that of the apparently aberrant.

The ornamentation consists of circular to oval rings with deep central pits. The ragged edges of the rings show, however, that they are of secondary origin, and since in some places the original scales are preserved, it is seen that the rings originate where the flat or slightly depressed top of the scales is broken away. The scales, where well preserved, strongly suggest the circular disklike scales so characteristic of Eusarcus. They might result from the compression of such wartlike scales as are present in the aberrant, and they may also lead to the droplike suboval scales of Echinognathus and of Stylonurus. The comparison with the latter genus is fortified by the presence of strong longitudinal ribs on the segment which is correctly considered by Mr Foerste as belonging to the postabdomen.

The genus Hughmilleria was erected by Sarle in 1902 for the common species of the Pittsford shale which is thought by its author to show close relation to Pterygotus though in many ways suggesting the genus Eurypterus. The following is the original 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 sternites, the last three being essentially like the corresponding dorsal plates. First sternite cleft for the reception of a median appendage, which varies in form according to sex. Basing sexual