CLASS II 



AEACHNIDA— XIPHOSUEA 



775 



called the Trilobite stage (Fig. 1500, B). After the first moult the caudal spine begins to 

 elongate, and at this stage, while tlie abdomen retains its segmented larval character, a true 

 affinity with the Paleozoic Frestwichia and Bclinurus is clearly revealed. The prevailing 

 modern view is that in Limulus we have a member of the Arachnida which retains its water- 

 breathing liabit, and, in the features of the abdominal appendages, some traces of the 

 characteristic structure of the primitive crustacean stock from which the Arachnida originally 

 sprang. 



The genus first makes its appearance in the Trias, one small species being known from 

 tlie Buntersandstein of the Vosges, and another, L. viccnsis Bleicher, from the Keuper of 



C, Limulus jiriscui 

 Miinst. Muschelkalk ; 

 Laineck, near Bay- 

 reutli. Vi- 



B, Embryo of Limulus, 

 ill the so-called "Trilo- 

 bite stage." Lateral 

 eves faintly .shown. 

 (After Dohni.) 



A, Limulus walchi Desm. Lithograjihic Stone; Solenhofen, Bavaria. 

 hitter showing several pairs of imi)erfectly preserved ambulatory limbs. On the carapace, covering the prosoma, 

 are seen impressions of the lateral eyes. 



Fic. 1500. 



Dorsal and ventral aspects, the 



Lorraine. L. loalchi is abundant in the Lithographic Stone of Bavaria ; L. nathorsti and 

 L. woodivardi are Jurassic species from Sweden and England respectively ; L. syriacus 

 occurs in the Cretaceous of the Lebanon ; and L. decheni occurs in the Oligocene brown coal 



of Teuchern, near Merseburg.^ 



Order 2. SYNXIPHOSURA Packard. 



Body elongated ; cephalothorax semicircular with more or less distinctly defined 

 m.cdian axis, and no facial sutures. Compound eyes generally present, ocelli not 



^ Biihm, J., tjber Limulus decheni Zincken. Jahrb. Preuss. Landesanst. Bergakad., 1905, 

 xxvi. One of these specimens described by Btilim represents doubtless the largest known 



vol 

 Limulus. 



