316 GEOLOGICAL SURVEY OF THE TERRITORIES. 
The telson is produced behind, with a long, broad, often spatulate 
plate or expansion, in A. glacialis, twice as long as the body of the tel- 
son itself; the end subacute, or broad and rounded, or bilobed; the 
edge smooth or spiny. The telson itself less spiny than in Apus. The 
caudal stylets, or cercopoda, about as in Apus. ; 
The principal generic differences are in the long produced telson, the 
shorter endites, the usually larger carapace, being larger in proportion 
to the body than in Apus (though not so in L. bilobatus), and with usu- 
ally only from 5 to 12 abdominal segments, besides the telson, projecting 
beyond the hinder edge of the carapace. 
Geographical distribution. — Western North America appears to be 
richer than Hurope-Asia in the species of this genus, one (L. productus) 
occurring in the EKastern Hemisphere, ranging from Central Europe to 
Scandinavia and England, while two species occur in the central zoo- 
logical province of the United States, and one in Greenland and Arctie 
America. No species of the genus have as yet cecurred in the Missis- 
sippi Valley or on the Atlantic coast, and none on the Pacific coast. 
Synopsis of the species. 
A. Endites 2-5 very short, not projecting beyond the carapace. Car- 
apace large; telson short, pointed, spiny on edge ..... LL. glacialis. 
B. Endites 2-5 rather long and slender, projecting well beyond the ear- 
apace. Carapace large, leaving only 5 abdominal segments and 
telson uncovered; telson long, spatulate ............- LL. couesir. 
Carapace very short; telson long, bilobed............-.-- LL. bilobatus. 
LEPIDURUS GLACIALIS Kroyer. 
Plates XVI, figs. 1 (enlarged nearly 3 times), la, 1b; XVII, figs. 1,5; XXI, figs. 1, 2. 
L. glacialis Kroyer. Naturhistorisk Tidskrift, 2d ser. vol. ii, 431. 1847. 
Carapace very large, narrowing somewhat toward the eyes, being 
more regularly ovate than in Z. cowesii, which is more elliptical ovate. 
The twelve terminal abdominal segments are left uncovered by the car- 
apace; the telson broad at the base and extended into a blunt prolonga- 
tion armed with coarse teeth on the edges, and as long as the telson is. 
broad at base; three sharp median teeth and a finely-denticulated tu- 
bercle on each side, at the base; the telson and its extension are smooth 
beneath. The cercopoda or caudal stylets are nearly as long as the 
body, slender and very hairy, rather than spiny. 
The appendages differ decidedly from the other American species in 
the 2d to 5th endites being very short and broad and more equal in size ; 
the 5th endite is much shorter than in the other species; the third and 
fourth of nearly the same size and length, and one-half as long as in the 
two other species; the second is about twice as large in proportion as 
in the two other species. The scale of the sixth endite is very long and 
slender, the tip much attenuated, with very long, hair-like set; the gill 
itself narrow, pear-shaped. . 
In the second pair of feet the second endite is twice as fares as in 
the two other American species; the third and fourth of about the 
same size as in the other species, while the fifth is about one half as 
long, the scale (6th endite) very large and ensiform, with the tip curved 
and ending ina spine, the inner e edge with sharp spinules, the outer edge 
with numerous long hairs. The accessory gill is inequilaterally triangu- 
lar, the proximal edge straight, not produced backwards, as in the other 
