THE EURYPTERIDA OF NEW YORK I8I 
Eurypterus dekayi Hall 
. Plate 19, figure 2; plate 20, figure r 
Eurypterus dekayi Hall. Palaeontology of New York. 1859. 3: 411%, 
pl. 82, fig. x | 
This species was based on a single specimen, now in the State 
Museum [pl. 20, fig. 1]. Its distinguishing characters are thus given in the 
original description: ‘‘ The entire body is proportionally shorter, the 
carapace shorter and broader than in E. remipes. ‘The swimming 
feet are shorter, and the terminal palette a little more developed than 
in E. remipes or E. lacustris, and the upper abdominal 
joints differ less from the thoracic joints in length, while the last one 
is alate on the two lateral edges, a feature not observed in any other 
species.” | 
_ The aspect of the type is that of a specimen which has distinctly 
suffered contraction by a shoving together of the segments and, mindful 
of the strange changes in aspect resulting from a pushing or pulling of 
the segments, especially in cast-off integuments, one might reasonably 
infer that all the above cited differences, save the alate lateral edges of the 
last segment, were largely of casual origin. The other specimen figured 
on plate 19 which is more favorably preserved, exhibits the same and 
additional distinctive characters while it is clearly but partially contracted 
in the preabdominal region and distended in the postabdominal. The most 
striking new character in this specimen is the presence of four to five long 
spines on each segment of the endognathites, instead of but one or two in 
all other members of the genus. The combined evidence of the two speci- 
mens leaves no doubt that we have to regard E. dekayi a peculiar 
aberrant type of Eurypterus. The following are the characters of this 
species: ) 
Description. Body of small size, short but broad and compact. The 
carapace is about one sixth the length of the body, the latter a little more 
than three times as long as wide. 
