222 



MANUAL OF ZOOLOGY. 



act as jaws, and have their free extremities developed into 

 daws ; 2. The possession of six abdominal pairs of appendages, 

 expanded for swimming, and carrying the gills -, 3. The posses- 

 sion of a semicircular buckler, covering the cephalothorax, and 

 carrying the eyes upon its upper surface ; 4. The possession of 

 a seQond buckler, or "operculum," covering the abdomen; 



Fig, 69. — Xiphosura, Litnulus polyphe- 

 mus, viewed from below, c The cephalic 

 shield carrying the sessile eyes upon its 

 upper surface ; o " Operculum," cover- 

 ing the reproductive organs; ^Branchial 

 plates ; a First pair of antennse (anten- 

 nules) ending in chelae. Below these is 

 the aperture of the mouth surrounded 

 by the spiny bases of the remaining five 

 pairs of appendages, which are regarded 

 by Woodward as being respectively, from 

 before backwards, the great antennse, the 

 mandibles, the first maxillae, the second 

 maxillae, and apairofmaxillipedes. All 

 have iheir extremities chelate. 



Fig. 70. — Eurypterida. Pterygoius An- 

 glictis, restored (after H. Woodward). 

 c c Chelate antennse ; o o Eyes, situated 

 at the anterior margin of the carapace ; 

 in. nt The' mandibles, the first and se- 

 cond maxillae;^ « n The maxillipedes ; 

 the basal margins of these are serrated, 

 and are drawn as if seen through the 

 metastoma or post -oral plate, which 

 serves as a lower lip. Immediately be- 

 hind this is seen the operculum or tho- 

 racic plate which covers the two ante- 

 rior thoracic somites. Behind this are 

 five thoracic and five abdominal somites, 

 and lastly there is the telson {f). 



5. The presence of a long, sword-shaped telson, or tail-spine, 

 articulated to the dorsal shield. 



. The larval Limulus does not possess the ensiform post-anal 

 spine of the adult, and is further stated to show a decided re- 

 semblance to the Trilobites. 



