H. Woodward—Eurypterus lanceolatus. Tek 
form of the abdominal segments, and the more lanceolate form 
of the telson, which in Pterygotus proper is broader, less acute, 
or even bilobed. The chelate antennules in Prerygotus are not 
adapted for palpi; but in both Eurypterus and Slimonia the 
basal joints of the simple antenne perform that office. 
Eurypterus differs, however, from both Pterygotus and Sh- 
monia in the position of the eyes, the form of the carapace and 
the telson, the form and number of the articulations of the 
swimming-feet, and lastly, in the structure of the thoracic 
plate. 
Dimensions of FE. lanceolatus. —The largest and smallest speci- 
mens known are in Mr. Robert Slimon’s collection: the former 
measuring 74 inches in length, and nearly 2 inches across its 
fourth and widest thoracic segment; the latter measuring 
only 14 inch in length by 2 across its widest segment. Mr. 
Wright’s specimen measures 63 inches in length; but is much 
distorted and compressed laterally. The length of the specimen 
in the British Museum is 44 inches, of which the head forms 
3 of an inch, the six thoracic segments 1 inch, the six abdominal 
segments 14 inch, and the telson 4 of an inch. The fourth 
thoracic segment is the widest, and measures 1 inch across; the 
succeeding segments taper gradually to the ninth, which is 
scarcely & of an inch in width; and at the twelfth segment the 
abdomen is only # of an inch wide. The first eight segments 
are of nearly equal depth, or about 4 of an inch; the ninth, 
tenth, and eleventh segments are about 2 of an inch in depth; 
and the twelfth more than 2 of an inch deep. The swimming- 
feet reach down to the fifth thoracic segment. 
The geological and geographical range have been already 
given by Mr. Salter, in the Geological Society’s Quarterly 
Journal ;* and Professor Hall’s monograph f contains a most 
beautiful series of illustrations of all the American species of 
this singular group, with careful descriptions. 
EXPLANATION OF PART OF PLATE V. 
Fig. 7. Upper side of Zurypterus lanceolatus (restored). 
8. Under side of same, showing the mouth, with the organs of mas- 
tication, prehension, and locomotion ; also the thoracic plate 
(¢ €) covering the branchial and reproductive organs. 
» 9. A single antennule enlarged, showing its broad serrated basal 
joint, which served as a foot-jaw, as did also the three suc- 
ceeding pairs of palpi and the basal joints of the broad 
swimming-feet (e e). 
” 
* 1859, vol. xy. p. 229. + Paleontology, New York, 1859, vol. iii. p. 397. 
