39-1 PALEONTOLOGY OP ILLINOIS. 



aware what characters were assigned it, or how its author proposed to distin- 

 guish it from the existing genus Limulus. Most authors, including Milne 

 Edwards, Bronn, Prestwich. Mantel], Portlock, Murchison and others, referred 

 the species to Limuhis, though Portlock, in doing so, remarks that the distinct 

 trilobation and segmentation of the abdomen in these fossil species, seem to 

 constitute a generic distinction. Pictet admits the genus in his Traite cle 

 Palseont., ii, 538, and remarks that it is distinguished from Limuhis "by the 

 articulation of the tail, and above all by the abdominal buckler presenting two 

 distinct longitudinal furrows." Prof. Owen also admits the genus in his valua- 

 ble Palaeontology, or Systematic Summary of Extinct Animals, p. 43, and says 

 it differs from the ''King-Crab (Limulus') in the movable condition of the body 

 segments." 



A careful study, however, of fine specimens of the species described below, 

 has satisfied us that the segments of its abdomen are not movable, but as firmly 

 and completely united into a single shield as in the genus Limuhis. We are, 

 therefore, led to believe that this genus is mainly distinguished from Limuhis 

 (so far as its characters have yet been made out) by the more transverse form 

 of its cephalo-thoracic shield, its proportionally much longer and more slender 

 legs,* the transverse or subcircular form and distinct trilobation and segmenta- 

 tion (not complete division, however) of its abdomen, as well as by its flattened 

 borders without movable spines. There are also some differences in the more 

 anterior position of the eyes, the stronger and more continuous character of the 

 ocular ridges, as well as in the subdivisions of the area included by these 

 ridges in Bellinurus. Other differences, of perhaps greater importance, will 

 probably be observed, when the appendages of the under side can be seen. 



None of our specimens are in a condition to show the small anterior pair of 

 simple eyes, though from the general analogy of this interesting crustacean to 

 the genus Limulus, it is more than probable better specimens may show them. 

 And yet it is possible, from the anterior position of the eyes, corresponding to 

 the larger reticulated pair in the genus Limulus, that the small supplementary 

 pair may not have been needed. As in Limulus, it shows a row of six small 

 pits in each of the longitudinal furrows of the abdomen, marking the position 

 of the muscular apophyses within; while the condyle, for the articulation of the 

 abdomen with the cephalo-thorax, seems to agree exactly with that of Limulus. 

 We are not aware of the nature of the peculiarities in the articulation of the 



*One of our specimens of the following described species, (as well as one of B. anthrax, 

 figured by Prestwich, Trans. Geol. Soc, London, v, p. xli, fig. 1), shows that at least 

 one pair of the legs (or possibly the antenna) must have been quite as long as the 

 abdominal and cephalo-thoracic shields together; which would be proportionally more 

 than twice the length of any of the legs or antennae in Limulus. 



