THE EURYPTERIDA OF NEW YORK 17// 
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. Ina well preserved adult the carapace measures 44 x 
63 mm; the preabdomen (slightly shortened). 51 x 72 mm; the first seg- 
ment measures 8.8 x 65 mm; the fourth 11 x 70 mm; the postabdominal 
segments measure respectively 8 X 51 mm; 12.7 X 42 mM; 14.5 X 37 mm; 
I§ X33 mm; 17.5% 27.5 mm; 20.5 x 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 X 71 mm; the preabdomen 60.5 x 80.5 mm; the post- 
abdomen 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 
13mm; 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 
EK. 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 de- 
termined.’’ 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- 
