80 
IOWA ACADEMY OF SCIENCES. 
The species in question which is of the general type of 
Encrinurus punctatus Wahlenburg, is well represented in the 
collections by two perfect, or nearly perfect, specimens and by 
scores of cephelons, moveable cheeks and pygidia, occurring 
both as external moulds and internal casts. 
The nearness of the fossiliferous stratum to the top of the 
quarry brought it well within the zone of weathering. The 
laminae of the rock were parted and the fossils thus disengaged 
with a single stroke of the hammer, and without any picking 
and cleaning that might mingle artificial with the delicate 
natural markings. The latter are exceptionally well preserved. 
To speak of the pygidia only, the caudal spine is shown in 
several specimens, the ninth pair of pleural are usually 
distinct, and even a tenth pair may sometimes be seen as min- 
ute ridges nearlj^ aligned with the axial lobe and ending upon 
it in a tubercle. Or the segmental lines on the mid-lobe as 
many as thirty- one have been counted with the aid of a magni- 
fying glass, and in seven specimens over twenty-five are thus 
visible, and in several specimens eight and even nine axial nodes 
have been observed. 
The investigation has thus been specially favored in the 
number and perfection of the specimens at hand. The promi- 
nence also of the large rounded anterior tubercle affords a sure 
ground which would be lacking if the investigation were 
carried over to the less distinct tubercles on the broad pleural 
annulations. In the same way the size of the specimens is of 
advantage. The largest twenty- three mm, in length and 
width, slightly exceeds in these dimensions the largest Encrin- 
urus the author has seen figured or described. From this size 
the specimens range to a minimum of eight mm. in length and 
breadth. In several of the smaller pygidia, the axial lobe is 
slightly more convex and the central longitudinal space 
between the discontinuous segments is more or less obscure. 
The first nine segments in especial, are plairdy continuous. 
While it is not thought that these are specifically distinct, they 
are separated in the following table by being marked with 
a star. Excluding these and considering the remainder whose 
specific identity can not be questioned, the following variation 
is observed; 
