298 



MANUAL OF ZOOLOGY. 



been slender five-jointed legs, in which the terminal segment 

 forms a pointed claw, and the basal segment carries a jointed 

 appendage, regarded by Mr Walcott as homologous with the 



Fig. 148. The skeleton of a" Trilobite (Angelina Sedgmickit), partially dissected. A, 

 Head-shield. B, Movable rings of the thorax. C, Tail or abdomen, g Glabella, in 

 this species without furrows ; fi Fixed cheeks ; e Eye - lobe ; o Eye ; f Facial 

 suture; fr Free cheeks: s Head -spines; / Pleurae; pp Anchylosed pleurae of 

 pygidium. 



" epipodite " of many recent Crustaceans. On each side of the 

 thoracic cavity there is, also, attached a row of bifid spiral 

 appendages (fig. 149, e\ of the nature of gills; and branchial 

 appendages were probably attached to the bases of the thoracic 

 limbs as well. With regard to the appendages of the head, 

 the mouth is situated behind the hypostome, and is bounded 

 by four pairs of jointed manducatory appendages, the basal 

 joints of which are, partly or wholly, modified to act as jaws. 



The cephalic shield of a typical Trilobite is more or less completely 

 semicircular (fig. 148), and is composed of a central and of two lateral 

 pieces, of which the two latter may, or may not, be united together in 

 front of the former. 



The median portion is usually elevated above the remainder of the 



