new Worm” from Lower Ludlow Beds. 125 
The American horizons are near the top of the Ordovician, 
and correspond approximately to our Lower Ashgillian. 
The original generic diagnosis is expressed in vague terms, 
and needs interpretation with aid of the figures and descrip- 
tions of the species. The actual length observed varies from 
1} inch (say, 28 mm.), as in a young P. covingtonensis, to 
6 inches (say, 152 mm.) in an example of P. tenuis. The 
actual width observed in the compressed fossils varies from 
“one fourth of a line” (say, 0°5 mm.), in the smallest P. tenuis, 
to about 2 mm., as seen in the figure of P. simplea. 
Owing to the incompleteness of most of the specimens, the 
ratio of width to length cannot be calculated with certainty. 
It is, however, possible to calculate the relative height of the 
segments, on the basis of such measurements as are provided, 
though these are not very precise :— 
Absolute height Ratio to 
of segment. width, 
PC MNGGNUA Cd es oe stews ’ 0°12 10/100 
Pe OFAUUMS AR ira ties ds 0°23 12/100 
P. covingtonensis ...... 015 15/100 
PY UTNEES & w dace ace hae es 05 33/100 
SE UOTEIG ae Ria «dae KES 05 50/100 
The nature of the segmentation is not clear. Ulrich’s 
figure of P. simplex (op. cit. pl.iv. fig. 4) probably represents 
the “ complete individual’’ mentioned on p. 91. This has a 
length of about 19 mm.,a greatest width of 2°7 mm., and 
tapers rapidly at each end. The drawing shows thirty-two 
segments, and, since the specimen is bent round so that one 
end almost approaches the other, these segments are lower 
on the inner side of the curve than on its outer, and the 
draughtsman has represented them as imbricating. This 
important feature is not alluded to in the text, nor is it 
suggested or mentioned under any other species. It would, 
of course, be particularly obvious in a form with the high 
and well-marked segments of P. simplex. 
The segments are papillate in P. ornatus and P. magnus ; 
in all other species, including the genotype, they are described 
as smooth. In P. ornatus the papille form either one row 
in the median line of a segment or one row near each border 
ofasegment. Ulrich’s enlarged figure 16 shows about twelve 
papille in each row, all closely set ; that means about twenty- 
five in the complete circle of each segment. In P. magnus 
** gach segment is ornamented with a single row of six or eight 
ee ” (a, e., twelve to sixteen in the complete circle). 
e pass now to the first record of the genus from this side 
of the Atlantic, and the first occurrence outside the Ordovician. 
