160 
IOWA ACADEMY OF SCIENCES. 
Pleuroxus sp ?. — The shell is long and low, in some specimens 
evenly arched from the posterior dorsal angle to a point a little 
in front of the brood chamber, from which the curve is flattened 
slightly to a distance including the basal third of the long sharp 
rostrum. In others the dorsal margin is evenly arched from 
the postero- dorsal angle to the rostrum. The head is small, 
high, with the long, sharp, curved rostrum far from the ante- 
rior margin of the shell, parallel with it, and reaching nearly 
to a line with the ventral margin of the shell. The ventral 
margin is straight for two-thirds of its length from the anterior 
margin; the remaining third curves gently upward and has a 
single small tooth pointing backward, a little in front of the 
sharp curve into the posterior margin. The ventral margin has 
long pectinated setso, becoming shorter toward the posterior 
end of the shell. The anterior margin has setae for a short dis- 
tance from the ventral margin. A blunt posteriorly directed pro- 
jection is formed by the postero -dorsal angle of the shell. 
The post abdomen is long, slender, truncate, tapering toward 
the end. The posterior edge is slightly concave, and is armed 
with eighteen to twenty or more small spines; the spines at the 
distal end of the series are much the longer and stronger. Anal 
claws are pectinated, long, and slightly curved. The second 
basal spine is longer than the first. 
The eye is of moderate size. Pigment fleck is about one-half 
as large as the eye, and is situated one-fourth the distance from 
the eye to the end of the rostrum. The antennules are cylindri- 
cal, with setae at the end, and a lateral seta. Length of anten- 
nules about equals the distance between the eye and the pig- 
ment fleck. Antennae are short, small, with long setae. 
The specimens do not agree in all respects with the descrip- 
tion given by Birge of Pleuroxus gracilis var. unidens, but do 
agree in many points. The largest specimen found measures 
.60 mm. in length by .38 mm. in height; another measures .60 
mm. long and .33 mm. high. Birge gives a measurement of 
.85 mm. by .46 mm., and states that the species is the largest 
yet seen. The original description of P. gracilis var. unidens 
states that, “the striation is very plainly marked.” The speci- 
mens found by the author are only very faintly striated, and 
that most distinctly at the anterior part of the shell, where the 
lines of striation are approximately parallel to the anterior 
margin. The larger part of the surface is free from markings, 
either striation or reticulation as far as could be observed. The 
