NATURAL SCIENCES OF PHILADELPHIA. 43 



We are likewise under obligations to Mr. Joseph Evans, of Morris, Illinois, 

 who first discovered the fossils at this locality, for the use of several speci- 

 mens. Amongst others, the form we have supposed to be a Caterpillar and 

 that we have referred to Anthrapalcemon, belonging to him. 



CRUSTACEA. 



ENTOMOSTRACA. 



XYPHOSURA. 



Genus BELLINURUS, Koenig. 



Not having had an opportunity to consult Kcenig's original diagnosis of 

 this genus, nor indeed a good description of it by any other author, we 

 are not aware what characters were assigned it, or how its author proposed 

 to distinguish it from the existing genus Limulus. Most authors, including 

 Milne Edwards, Bronn, Prestwich, Mantell, Portlock, Murchison and others, 

 referred the species to Limulus, though Portlock in doing so remarks that the 

 distinct trilobation and segmencation of the abdomen in these fossil species, 

 seem to constitute a generic distinction. Pictet admits the genus in his 

 Trait de Palceont., ii. 538, and remarks that it is distinguished from Limulus " 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 

 valuable " 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 Limulus. We 

 are, therefore, led to believe that this genus is mainly distinguished from Lim- 

 ulus, (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 transversely or subcircular form, and distinct trilobation 

 and segmentation (not complete division, however,) of its abdomen ; as well 

 as by its flattened borders without movable spines. There are also some dif- 

 ferences in the more anterior position of the eyes, the stronger and more con- 

 tinuous character of the ocular ridges, as well as in the subdivisions of the 

 area circumscribed 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 more 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 LAmulus, 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 cephalothorax, seems to agree 

 exactly with that of Limulus. 



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

 the caudal segment mentioned by Pictet, none of our specimens being in a 

 condition to show the connection of these parts satisfactorily, while he does 

 not explain in what the difference consists. 



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

 by Prestwieh, (Trans. Geol. Soc, London, v. p. xli. fig 1,) shows that at least one pair of the legs 

 (if they were articulated around the mouth, at the middle of the cephalothorax, as in Limulus) 

 must have been quite as long as the abdominal and cephalothoracic shields together; which would 

 be proportionally more than twice the length of any of the legs in Limulus. 



1865.] 



