280 Dr. H. Woodward—Eurypterus in the Coal-Measures. 
depth. These seven segments forming the thorax (pereion of Spence 
Bate) give to the body a somewhat globular or rounded contour. 
Those which follow (probably seven in number) were greatly reduced 
in breadth, but increased somewhat in depth, ending in all probability 
in a more or less long slender ensiform telson. Figs. 1 and 2 have 
only eight and nine segments respectively preserved, the remainder 
of the abdominal series, which extended into the matrix beyond the 
edge of the clay-ironstone nodule, being lost. 
In Hurypterus, as in so many other Arthropods, each somite is 
elothed in a chitinous or caleareo-chitinous envelope, an upper part 
(or tergum) and a lower part (or sternum) giving rise at their junction 
to small recurved epimeral plates or pleure on the lateral margins 
of each segment. These tergites and sternites, in fossilisation, have 
been pressed together, and are often somewhat displaced along the 
margins of the segments, but the outer upper surface can always 
be readily detected by the presence of rows of minute squamate 
markings so characteristic of all the Merostomata (see Figs. 1 and 2). 
Although the head-shield in Fig. 2 is less well preserved than that 
of Fig. 1, and the eyes are very indistinct, there are portions, nearly 
in place, of at least four jointed endognaths or palpiform organs 
(en. 1, 2, 3, 4), which served as mouth organs and also as locomotory 
appendages, the last and most posterior pair, which are always the 
largest, being modified to serve as powerful swimming feet. Probably 
en. 3 and 4 may represent this pair of swimming feet, one of which 
has been in that case displaced from the right side. The basal joints 
of this posterior pair occupy in Fig. 2 the same position as in Fig. 1, 
being placed one on either side of the oval metastoma. ‘The greater 
part of the opercular plate (op.), situate immediately behind the head, 
is exposed to view by the removal of the tergites of the first and 
second body-segments, leaving the left side and the central appendage 
uncovered. Two of the series of narrow abdominal segments following 
the broad thorax are preserved in Fig. 2; also the pointed recurved 
pleurze or epimera on the right side of the seven thoracic plates, which 
are well shown and quite in order. 
In the figures given by Professor James Hall of the American - 
Eurypterus Mansfieldi from below the Cannel Coal, Cannelton, Pa., the 
epimeral pieces on the margins of the body-segments are shown to 
be produced into strongly recurved spinous processes (see particularly 
op. cit., pl. iv, fig. 3, and pl. v, figs. 3 and 11). . These spinous 
lateral processes also frequently occur detached, and I have seen such 
from our own Coal-measures, but I do not think they were so prominent 
on the segments of Hurypterus Moysey?. 
Measurements.—Fig. 1. Length of head-shield 21 cm., breadth at 
base 26cm.; breadth between eyes at back 10 cm., length of eye 
4cm.; length of metastoma 10cm., breadth 8 em.; length of median 
appendage to opercular plate 12 cm., breadth 4em.; length from base 
of metastoma to base of 7th segment 21cm.; greatest breadth of 
thorax 29 cm., average depth of thoracic segments 5}cm.; breadth of 
first abdominal segment 15 cm., depth 7 cm. 
Fig. 2. Length of head-shield 17 cm., breadth of base 23 cm.; length 
of seven thoracic segments 25 cm., greatest breadth 26 cm.; length of 
