NATURAL SCIENCES OP PHILADELPHIA. 45 



the matrix for a distance of about 0-30 inch, being slightly curved near the 

 extremity, and apparently tapering to a point, this was probably also pro- 

 vided with a movable finger as in Limulus, but the specimen is not in a con- 

 dition to show it. It is not possible to determine which one of the legs this is. 



Entire length from the extremity of the caudal segment to the anterior 

 margin of the cephalo-thorax, about 1-90 inches. Length of cephalo-thorax, 

 0-51 inch, breadth of do. to the extremities of postero-lateral spines, 1-70 

 inches ; length of area included within the ocular ridge, 0-50 inch ; greatest 

 breadth of do. (which is the distance between the eyes,) 0.60 inch. Length 

 of abdomen, 0*65 inch ; breadth of do., exclusive of the flattened margin, 0-94 

 inch, including it, 1-06 inch; breadth of mesial lobe, 0-23 inch ; length of 

 caudal segment, about 0-60 inch. 



Of the known species of Bellinurus, ours seems to be most nearly related to 

 B. bellulus, Koenig, (the type of the genus, if we mistake not), which is re- 

 garded as being identical with Limulus rotundatus, of Prestwich, (Trans. Geol. 

 Soc, London, v. p. 413, pi. XLI. figs. 4, 6 and 7.) From this species, however, it 

 may be at once distinguished by having the lateral angles of its cephalo-thorax 

 produced into long, slender spines, and the flattened border of its abdomen 

 proportionally much narrower, and armed with a series of sharp-curved 

 spines, instead of being merely serrated. 



We should also remark here, that Prof. Owen's figure of B. bellulus, (Palae- 

 ontology, p. 42,) as well as that given by Murchison of the same, under Prest- 

 wich's name rotundatus, (Siluria, p. 318,) represent the eyes as being located 

 at the lateral extremities of a large, transversely oval or subelliptical area ; 

 while within this, there is a smaller, crown-shaped area, circumscribed by a 

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

 species has the eyes located at its anterior lateral angles. This wide dif- 

 ference 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 impro- 

 bable 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 are with difficulty seen in any but well preserved specimens) in 

 this outer position, and the presence of a large outer ocular area surrounding 

 that corresponding to the quadrangular one in our species. We are the more 

 inclined to think this is the case, from the fact that Owen's and Murehison'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 cen- 

 tral 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 Crea- 

 tion, p. 550,) which show no traces of this outer transversely oval ocular 

 area. 



In the elongated, spine-like character of the lateral angle 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. anthrax (= 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 ab- 

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

 anthrax and B. bellulus. 



We are gratified to be able to dedicate this fine species, the first of the 

 genus hitherto discovered in America, 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 fore- 

 going description was drawn up. 



1865.] 



