Eurypterus lacustris Harlan 
Page 173 
See plates 9, 10, 12, 13 
1 Young individual. Original of Hall’s figure [Palaeontology of N. Y.., 
v. 3, pl. 81, fig. 1] x 2. Shows well the outline of the carapace and 
the relatively large size of the compound eyes in the young. The 
preabdominal segments are shoved together, and the preabdomen 
appears therefore too short and wide and too abruptly contracted. 
The apparent posterior edges are partly fracture lines. The outline 
drawing of the specimen, inserted in the text, shows this condition 
more distinctly. 
2 Ventral side of a specimen, showing the five sternites with their median 
sutures. The first four retain a certain amount of uniform convexity, 
the fourth is pushed inward and much arched, the fifth flattened 
and shows the relatively great length of these segments. The genital 
appendages of the first (opercular) and second sternites are broken 
out, leaving a cleft. Natural size 
3 Operculum, original of Hall’s figure, op. cit. pl. 81, fig. 8 [see diagram, 
text fig. 122]. The pentagonal pieces in front of the opercular appendage 
are seen. The principal median appendage is broken at b, its original 
extension indicated by an impressed line at c. The paired tubular 
Text fig. 122 Diagram to pl. 11, fig. 3 
appendages are recognized in outline at a, and the aperture seen at h. 
The posterior (¢) and lateral (d) doublures, as well as fragments of 
the anterior connecting membrane, are also shown. Natural size 
462 
