the appearance of which may, however, be due to secondary changes in the substance of the integument, which gave it partly a scaly, partly a granular character. Some apparently well preserved portions of the integument are quite smooth.
Measurements. The type which is also the largest specimen, measures 295 mm. The carapace is 65 mm long and 73 mm wide at its widest part and 61.5 mm wide at the base. The eye had a longitudinal diameter of 13.5 mm. The preabdomen measures 42.5 mm in length and 61 mm in width; the postabdomen 96.6 mm in length and 53.5 mm at its beginning and 18 mm at its end. The length of the first postabdominal segment is 8 mm, that of the last 29 mm. The telson is 91 mm long and 7 mm wide. The third limb projects about 51 mm beyond the carapace, the fourth about 82 mm, the last about 135 mm. In a young specimen the total length is 93 mm, the carapace measures 21.5 × 24 mm, the preabdomen 18 × 22 mm, the postabdomen 31 × 16.5 mm (31 mm width at beginning and 6 mm width at end); the telson 23 mm. The fourth limb projects 26 mm, the last 44 mm.
Horizon and locality. Kokomo limestone of Kokomo, Indiana. Types (four specimens, nos. 12903 (holotype), 12904, 12908, 12911) in the University of Chicago collection.
Remarks. Drepanopterus longicaudatus is a unique form among the American eurypterids being the sole representative thus far found on this continent of this rare and phylogenetically interesting genus. From its Scottish allies, it is readily distinguished by its slender and elongated postabdomen and the long, clavate telson.
Two of the four specimens before us are only one third the size of the others, thus representing much younger stages. Nevertheless, their habitus and relative dimensions do not differ from those of the older as one might expect. This is especially obvious in the comparative lengths of the appendages and the telson to the whole body. In both the old and the young, the length of the last limb to that of the body is as 7 : 15 and that of the preceding limb to the last one as 3 : 5.
