1855.] SALTER HIMANTOPTERUS. 27 



as to suggest immediately an affinity between tliat large Crustacean, 

 with strong didactyle pincer-like feet, and these with the principal 

 feet, at least, adapted for swimming (" ruderblattchen"). The 

 entire form of Pterygotus, however, is so little known, that it is 

 impossible to say it did not possess a pair of natatory feet *, and large 

 pincer-like antennae ; and, on the other hand, the anterior pair in 

 our fossils are chelate organs, and nearly all the figures of Eurypterus 

 show something of the same kind. The affinity then with Pterygotus 

 may be closer than we yet know of. 



EurypteruSi De Kay, is a large and elongated Crustacean, with an 

 entire semioval or subquadrate carapace, on which the large sessile 

 eyes are placed, in the manner of those of Limulus, wide apart, but 

 towards the middle of the head. The body is ovato-lanceolate, broad 

 in front and attenuated behind, and terminated by a pointed or acu- 

 minated tail. There are 10 or 11 body-joints, exclusive of the tail- 

 joint ; and the hinder (abdominal) rings are subquadrate ; the ante- 

 rior (thoracic) rings widely transverse. 



The limbs or appendages are three on each side, according to the 

 very perfect figures given by Eichwald ; the two anterior of which 

 are simple appendages, of about five joints each, with small chelate 

 tips. The hindermost pair are much broader and longer, consisting 

 of five joints, of which the two terminal ones are rather suddenly 

 dilated and form a long-oval palette. 



HiMANTOPTERUS, gCU. UOV. 



In the specimens here described, although the general form is 

 much the same as that of Eurypterus, there is this essential difference, 

 that the eyes are placed, not on the surface of the head, but on the 

 anterior or antero-lateral margin, and quite at the edge. Together 

 with this, the swimming feet are of a more linear form or rather 

 thong-shaped. The name Himantopterusf maybe therefore appro- 

 priate for the genus to which these specimens belong. 



They are closely allied to Eurypterus, like which they have a 

 comparatively small carapace, with the single pair of maxillary feet 

 for swimming, but, so far as we yet know, with only one pair of 

 antennae. These latter organs are linear, narrower than the paddles, 

 and consist of few joints ; the last joint is strongly didactyle, with 

 rather long chelae. The accompanying woodcut (p. 28) shows the 

 general characters of the genus. 



A genus nearly allied to this has been described by H. von Meyer 

 and Dr. Jordan, from imperfect specimens in the coal of Saar- 

 bruck;]:. Von Meyer's genus differs at a glance from our fossils in 

 the sudden reduction of width in the abdominal joints ; there are 



* Agassiz's figure of the principal limb (Poiss. Foss. Vieux Ores Rouge, tab. A) 

 looks exactly like one of the swimming feet of Himantopterus : and the very large 

 pincer-Uke limbs in that case must surely be antennae. 



t From the Greek ifias, lixdvros, a thong, and Trrepov, a wing. 



J Dunker and Von Meyer's Palaeontographica, vol. iv. pt. 1. p. 8. pi. 2. fig. 1. 



