represents about the youngest stage known as yet in an entire specimen. This is here reproduced by photograph on plate 11, figure 1 [text fig. 36]. This specimen exhibits the somewhat larger size of the eyes and the more compact form of the body. It must, however, be remarked that the body shows evidence of compression axially.
Measurements. In a well preserved adult the carapace measures 44 × 63 mm; the preabdomen (slightly shortened) 51 × 72 mm; the first segment measures 8.8 × 65 mm; the fourth 11 × 70 mm; the postabdominal segments measure respectively 8 × 51 mm; 12.7 × 42 mm; 14.5 × 37 mm; 15 × 33 mm; 17.5 × 27.5 mm; 20.5 × 22 mm. The eyes are 4.7 mm long. The telson spine is 64 mm long and 12.5 mm wide at its anterior extremity. The fourth endognathite projects 41.5 mm beyond the edge of the carapace, the swimming leg 70 mm. In another specimen the carapace is 49.5 × 71 mm; the preabdomen 60.5 × 80.5 mm; the postabdomen is 88 mm long and measures 56.5 mm at its anterior extremity and 20 mm at the posterior one. The telson is incomplete. The eyes are 8.5 mm long; the first endognathite projects 8.5 mm; the second 13 mm; the third 21.5 mm; the fourth 35.5 mm; the swimming leg is 75.5 mm long.
Horizon and localities. E. lacustris occurs typically only in the Bertie waterlime quarries at Williamsville and Buffalo, N. Y. and Bertie, Ontario. A few smaller specimens also have been obtained at Black Rock, Erie co. and Union Springs, Cayuga co.
Remarks. In regard to the differences between E. remipes and E. lacustris, Hall makes this statement: "This species differs from E. remipes in its greater size, and less abrupt attenuation toward the tail, while the carapace is proportionately broader and shorter. There are likewise differences in the anterior feet, and in the form of the postoral plate; the entire form of this latter appendage not having been fully determined." We see the principal distinctive character in the greater width of the carapace, the proportion of length to width in E. remipes being as 6 : 7 (with 8.5 as maximum) and E. lacus-
