HIGH SCHOOL ZOOLOGY. 



201 



15, On the Atlantic coast, from Nova Scotia southwards, 

 there occurs a very remarkable animal called, on account 



of its shape, the horee-shoe crab, Limu- 

 lus 'polypliemns (Fig. 133), the body of 

 which is divisible into thi-ee regions — 

 cephalothorax, abdomen and caudal spine. 

 The first of these bears six pairs of leg-like 

 appendages, chiefly chelate, on either side 

 of the mouth, possibly equivalent to the 

 first six jiairs of the Crustacean. The ab- 

 dominal appendages are present in five 

 pairs, the outer branches of which are 

 beset with gill-leaflets. Limixlus passes 

 through a " Trilobite-phase" (Fig. 134), in 

 its development, so called on account of 

 its resemblance to the singular fossil Ar- 

 Limxilvs pohjphcmus. \. thropods, which were so abundant during 

 the Palaeozoic period. (Fig. 135). 



Fisr. 133. 



Fi<r. 134.-Trilobite-)hase 

 of Liinulus. 



(After King-sley). 



Fig. 135. — Asaphhus Canatlensis. 

 Chapman. Utica Foimation. 



16. Both the Trilobites and Limulus have generally been 

 considered as Crustacea, but many points in the structure and 

 14 



