from the doublure of the carapace, but no epistoma is formed. The metastoma is oval in outline, but slightly emarginate in front. The tergites and sternites are more or less bandlike and plain as in other genera; the male opercular appendage is small, with simple median lobe; that of the female long, extending to the third sternite and beyond, consisting of two paired and two single members, the paired members forming two pentagonal basal pieces, and two clawlike terminal pieces. The single imbricating lobes form the long median part. They are produced into lateral points at their posterior extremities. Two curved, interior tubes are connected with the female organ. The postabdominal segments are bandlike rings. The telson is long, spinelike, flat on the dorsal side and carinate on the ventral side.
Several species which have currently been brought under Eurypterus are here shown to belong to Eusarcus and to differ in a number of characters of generic value, viz, the form of the carapace which is triangular, the marginal position of the compound eyes, the decrease backward of the endognathites and the spinosity of all legs, the form of the metastoma, which is subtriangular and the broad and flat preabdomen. The differences of Eurypterus from the other genera are well known and for the most part manifest. They consist principally in the position of the lateral eyes, the absence of distinct facets, the different development of the chelicerae and endognathites, the form of the metastoma, of the opercular appendages and of the telson.
The North American species are given in the following list, those found in New York being distinguished by an asterisk. The list is in ascending order.
| Lower Siluric | Upper Siluric |
| FRANKFORT SHALE | CLINTON BEDS |
| *E. megalops nov. | *E. prominens Hall |
| *E. pristinus nov. | KOKOMO WATERLIME—(=Lockport) |
| *E. ?(Dolichopterus?) stellatus nov. | E. kokomoensis Miller & Gurley |
| E. ranilarva nov. |
