398 PALAEONTOLOGY OF ILLINOIS. 



ridge, and in all its principal features corresponding to that which in our spe- 

 cies has the eyes located at its anterior lateral angles. This wide difference in 

 the position of the eyes, as well as in the ridges of the central region of the 

 cephalo-thoracic shield, if they really exist, would apparently be of more than 

 specific importance. The close general agreement, however, of these forms, in 

 all their other essential characters, renders it very improbable that they belong 

 to different genera. Hence, we would suggest that there may have been some 

 error in the figures cited above, representing the eyes (which ar^with difficulty 

 seen in any but well preserved specimens) in this outer position, and the pre- 

 sence of a large outer ocular area surrounding that corresponding to the quad- 

 rangular one in our species. W.e are the more inclined to think this is the 

 case, from the fact that Owen's and Murchison's figures appear to have been 

 reduced from Prestwich's figures 5 and 6, cited above, which represent the two 

 halves of a nodule, containing a specimen and its mould, of B. bellulus, with a 

 large transversely oval space in the central region of the cephalo-thorax, as we 

 must think, accidentally crushed in. This view seems to be sustained, too, by 

 Mantell's figures of the same species, from specimens collected by him at the 

 same locality (see Medals of Creation, p. 550), which show no traces of this 

 outer transversely oval ocular area. 



In the elongated, spine-like character of the lateral angles of its cephalo- 

 thoracic shield, as well as in having the margins of the abdomen armed with 

 sharp spines, our species agrees more nearly with B. anihrax{= Limulus an- 

 thrax, Prestwich), but it differs in the form of the outline of the anterior side 

 of the cephalo-thorax, as well as in the direction of its prolonged lateral angles, 

 and its less produced spines around the flattened margins of the abdomen. 

 Hence, it appears to be intermediate in its characters between B. anthrax and 

 B. bellulus. 



This fine species, the first of the genus discovered in America, was with 

 great pleasure dedicated by us to Prof. James D. Dana, the author of one of 

 the most important works on the Crustacea ever published ; to whom we are 

 indebted for the loan of one of the specimens from which the foregoing descrip- 

 tion was drawn up. 



Locality and position: Morris, Grundy county, Illinois; near the base of the 



Coal Measures.* 



. • 



* By an oversight, the position of the Batrachian described from this bed, on p. 135, 

 is wrongly given, in a note at the bottom of that page, as above the fliiddle of the Coal 

 Measures. 



