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NEW YORK STATE MUSEUM 
The metastoma is very similar to that of E. remipes, but subject 
to some variation and frequently somewhat contracted in the posterior 
portion [pl. 11, fig. 
5], giving it a more slender appearance. 
The female genital appendage was very correctly figured by Hall 
[loc. cit. pl. 81B, 
fig. 4]. Several well preserved specimens before 
us show the great size attained by this organ in mature 
Sa individuals. It reaches with the long paired, hornlike 
Figure 35 Euryp- 
terus lacustris 
Harlan. Cast of in- 
terior of proximal por- 
tion of female oper- 
cular appendage 
terminal appendages, to the posterior edge of the third 
sternite. The interior tubular appendages of this organ 
are finely seen in the original of plate 12, figure 2, 
where the integument has broken away. They have 
the precise form and relative proportions of that of 
E.remipes. The appendage of the second ster- 
nite has not been seen unobscured by the overlying 
appendage of the operculum. It is, however, well shown 
in the interior view, reproduced in plate 11, figure 4 
[Hall’s type of pl. 81, fig. 6]. It is extremely slender 
and pointed and reaches nearly as far back as that of the 
operculum. The male appendage does not differ from 
that of the preceding species. | 
Ornamentation. As far as our observation goes, the 
ornamentation is quite hke. that of E. remipes. 
This is especially notable in regard to the series of scales 
on the dorsal side, already correctly figured by Hall 
[pl. 81B, fig. 1]. The smaller scales which are rarely 
seen, are crescent-shaped to subtriangular and nowhere 
densely crowded. Those of the longitudinal series were 
Figure 36 Euryp- 
terus lacustris 
Harlan. Young indi- 
vidual. Reproduced 
on plate 11, figure 1. 
Natural size 
larger and circular in the anterior portion, becoming elongate in the pos- 
terior part of each row. 
Ontogeny. But little is known of the ontogeny of this species as 
but very few young individuals have been obtained and these are too far 
developed to afford much information. Hall’s figure, [plate 81, figure 1], 
