FOSSIL FORMS 279 



In Neolimulus, JBelinurus, and Prestwichia, lateral eyes are 

 present on the sides of the axial parts of the carapace, and near 

 its front margin median eyes have been found in the two last- 

 named genera. 



In nearly all the specimens of Palaeozoic Xiphosura ^ which 

 have been found nothing is seen but the dorsal surface of the 

 body ; in only a very few cases have any traces of the append- 

 ages been seen/ but, so far as known, they appear to have the 

 same general character as in Limulus. 



Aglaspis, found in the Upper Cambrian of Wisconsin, has 

 been regarded as a Xiphosuran. If that view of its position is 

 correct, then Aglaspis will be the earliest representative of the 

 group at present known. Other genera of Palaeozoic Xiphosura 

 are Bunodes, Bunodella, and Pseudoniscus in the Silurian ; Pro- 

 tolimulus in the Upper Devonian ; and Prolimulus in the 

 Permian. 



1 The British fossil forms of this group are described and iigured by H. Wood- 

 ward, "Monograph of the Merostomata," Palaeontogr. Soc. 1866-78, and Geol. 

 Mag. 1907, p. 539. 



'^ Packard, "Garb. Xiphos. K America," i/em. Nat. Acad. Sci. WasMngton, 

 iii., 1885, p. 146, pi. vi. fig. la, pi. v. fig. 3a (restoration). Williams, Amer. 

 Jmrn. Sci. (3), xxx., 1885, p. 45. Fritsch, Fauna d. Gaskohle, iv., 1901, p. 64, 

 pi. 155, figs. 1-3, and text-figures, 369, 370. 



