252 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
Schoedler. I must here express my suspicion that the Plewroxus 
aculeatus, P. exiguus and P. excisus all belong under this species. I 
‘have seen a small form which lacked the fine striations; and there ap- 
peared to me to be, at times, a slight indication of a second series of 
hairs upon the post-abdomen. 
The form is oblong, truncate behind, variously arched above, but 
usually with a rather low, evenly curved dorsal contour; the lower 
shell margin is either nearly straight or convex in front and concave 
along the posterior third, and is heavily beset with very long pectinate 
bristles. The head is moderately depressed, with a very broad, blunt 
and short beak (in some positions this beak seems acute, but it is an 
optical delusion); the fornices are very broad, covering the antennules 
completely; seen from above the head is broad and truncate in front; 
the eye is larger than the large pigment fleck, which is nearer it than 
the end of the beak. The antennz have eight setz, the last of which 
is minute; the five spined ramus has a strong thorn on the end, and 
the inner terminal seta is reduced. The post-abdomen is rather broad 
and truncate or somewhat rounded below; its length is very variable, 
being short in small individuals; its form is subject to concomitant 
variations. Theseven to eleven anal spines extend in a series of minute 
bristles above the anus. The lower posterior angle of the shell bears 
one to four teeth; the marking consists of wavy ridges and strie, pro- 
ducing, by the crossing of two sets springing from the two lower angles, 
a reticulation covering more or less of the entire shell. The head-shield 
and the spaces between these markings are densely striated. Color 
yellowish, often opaque. Length 0.24 to 0.40 mm. At times abund- 
ant. Birge alone has seen the males; his description agrees with Kurz’s 
account of the male of 4. exigua, save that the former speaks of spines, 
and the latter of thorns, along the post abdomen. 
Alonella exigua Lilljeborg. 
Lynceus exiguus—Lilljeborg, Leydig, Fric. 
Pleuroxus exiguus—Schoedler, P. E. Mueller. 
2 Lynceus aculeatus—Fischer. 
Aside from the differences in the male sex as above indicated, this 
form is said to have a convex lower margin, a rounded post-abdomen, 
and the pigment fleck nearer the end of the beak than the eye. The 
absence of the fine striation, finally, is the most marked characteristic: 
Length 0.30 to 0.83 mm. Not identified in America. 
(?) Alonella grisea Fischer. 
This species is included here on the authority of Kurz. The shell 
may or may not be toothed at the lower corner, and is partly lined and 
partly reticulate; but the only character which at all separates this 
