ON THE CARBONIFEROUS XTPflOStlROUS FAUNA. 149 



angle of the glabella, in a position homologous with their situation in Limulus. I venture then to 

 give the oi^inion that the apparent diflferences between Prestwichia and Euproops, as stated by 

 Messrs. Meek and Worthon, did not exist in nature, and that the genus Prestwichia was common 

 to botii Europe aiul North America during the Carboniferous Period. It is interesting in this 

 connection to observe that the descendants of the BelinuridfB in Europe, survive in the Solenhofen 

 Limuli until the Jurassic, and disappear daring the Cretaceous period, not to arise again on the 

 western coasts of the old world, while in North America, so far as the record shows, the type became 

 extinct during the Mesozoic and Tertiary, to reappear in the Quaternary and ])resent period. 



As regards the differences between Belinurus and Prestwichia, the former genus is the higher 

 form, approximating Limulus in the consolidation of the eighth and ninth abdominal segments 

 (forming the "abdomen" so regarded by Dr. Woodward) and in the very long caudal spine. In 

 Prestwichia there is one abdominal segment less than in Belinurus, the short caudal spine forming 

 the eighth. 



Belinurus laooei Packard. PI. V, fig. 5. 



Belinunis lacoei Pack., Amer. Naturalist, xix, '292, March, 1885. 



Cephalic shield of the usual shape and length in proportion to the abdomen ; the front margin 

 as usual ; the genal spine long, acute, extending obliquely outwards to a point parallel with one 

 either a little behind the middle of the abdomen, or, in the older, larger .specimens, nearly to a 

 point parallel with the base of the caudal spine. The median lobe is, as usual, divided by the 

 median line into two sublobes, so that the front edge of the entire lobe is indented in the middle ; 

 each sublobe contracts in width posteriorly behind the ocular or lateral angle bearing the com- 

 pound eyes. The ocelli are not visible, but the compound eyes ai'e partly preserved ; they are 

 small, and of the usual kidney shape. The abdomen is much more rounded than in the European 

 B. regince, being twice as broad as long. It consists (including the caudal spine) of nine seg- 

 ments. The median lobe is as broad at the end as at the base next to the thorax ; there is a 

 median tubercle on each segment, those on the third and last segment being larger than the 

 others. The margin of the abdomen is broad and thin, giving rise to broad, acute, lateral spines. 

 The caudal spine is very long and slender, a little swollen at the base; it is also triquetal, as in 

 Limulus; it is nearly one-half longer than the body, i. e., longer than the whole body by the 

 length of the head, and ending in a fine, slender, needle like point. 



Length of the best preserved specimen SS""'" (including the caudal spine). 



Length of body, 15™™. 



Length of caudal spine, 18™™. 



Length of cephalic shield, 7™™ ; breadth at base of lateral spine, 16™™. 



Length of lateral spine, 4-5™™. 



Length of abdomen, 8™™; breadth (not including the spines), 12™™. 



In nodules at Mazon Creek, Illinois; Nos. 210'", 210y, 210"% 212**; 213», collection of Mr. Lacoe. 



While having the same number of abdominal segments, this species, the first representative 

 of the genus which has occurred in America, diS'ers from B. regince chiefly in the more rounded, 

 less triangular outline of the abdomen, and in the smaller lateral abdominal spines. It is prob- 

 able that in Dr. Woodward's figure of B. regince the compound eyes are not correctly placed. In 

 our specimens of Belinurus they have the same relative situation as in Prestwichia dame and 

 longispina. 



