PROCEEDINGS OF THE \ \TI<>\ \l. \1USEI !/. vol. 38. 



peduncle of third uropod and cleft (typically) nearly two-thirds of 

 the distance to base. The difference in the two species as regards 

 the ratio of the length of peduncle of third uropod to the length of 

 telson is constant in the newly hatched young as well as in the largesl 

 adult (see table . 



In E. gracilis the third, fourth, and fifth perseopods have their 

 basal joints serrated along the posterior margins but the spines are 

 longer than the adjacent teeth. In E. serratus the depths of the 

 serrations vary, hut in all specimens examined the teeth were much 

 longer and more acute than those of K. gracilis and about twice the 

 length of the spines between them. 



The propodi of gnathopods one and two are proportionately longer 

 in /:'. serratus, the palms more oblique and more convex, and the 

 carpus of second gnathopods never longer than broad. 



Six segmenting eggs of E. gracilis were measured and an average 

 size of 0.256 by 0.334 mm. was obtained, which was less than the 

 same for E. serratus. 



Habitat. -The type-specimens were collected March 11, 1908, from 

 the marginal vegetation of 'Railroad Pond," about H miles north 

 of Ashland. Virginia. They were especially abundant in the thick- 

 est patchesof Sphagnum and Utricularia at depths varying from a few 

 inches to ll feet. Associated with them were large numbers of /•.'. 

 gracilis and HyaleUa Tcnickerbockeri (Bate). 



Differences between >/<>un(/ and adult. — It was thought that by com- 

 paring the structures in the young of E. serratus with those of the 

 adult and also with those of the young of E. gracilis, some Light would 

 be thrown upon the status of the former as a distinct species. Ac- 

 cordingly several young, differing not more than a day in age. were 

 taken from the marsupial pouches of individuals of each form, the 

 various appendages dissected, stained in aqueous eosin and mounted 

 I'm- microscopical examination. 



The young of K. serratus were found to differ from their parents in 

 the following particulars : 



(1) First antenna (fig. 9): Primary flagellum composed of but 

 four segments all proportionately longer than those of the adult. 



Second antenna (fig. 8): Flagellum composed of but three 

 mentis. 



First gnathopod dig. 10): Greal angularity of the region at the 

 junction of the palm and the posterior margin of propodus. The 

 latter is proportionately smaller and its posterior margin destitute 

 of spines and ha'us. The palm is straight, less oblique and thickly 

 covered on both sides with minute sharp teeth. These teeth are 

 much more evident in the voting than in the adult, 



