188 



MANUAL OF ZOOLOGY. 



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

 sion of a semicircular buckler, covering the cephalothorax, and 



''0 



Fig. 53. Xiphosura. Limulus polyphemus, 

 viewed from below, c. The cephalic 

 shield carrying the sessile eyes upon its 

 upper surface ; o. ' Operculum,' covering 

 the reproductive organs ; b. Brancliial 

 plates ; a. First pair of antennas (anten- 

 nules) ending in cheke. 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 antennas, 

 the mandibles, the first maxillas, the se- 

 cond maxilke, and a pair of maxillipedes. 

 All have their extremities chelate. 



Fig. 54. Eurypterida. Pterygotus Angli- 

 cuf, restored (after H. Woodward), 

 c c. Chelate antennas ; o o. Eyes, situated 

 at the anterior margin of the carapace ; 

 m m. The mandibles, and first and second 

 maxillae ; n n. The maxillipedes ; the 

 basal margins of these are serrated, and 

 are drawn as if seen through the meta- 

 stoma or post-oral plate which serves 

 as a lower lip. Immediately behind this 

 is seen the operculum or thoracic plate 

 which covers the tAvo anterior thoracic 

 somites. Behind this are five thoracic, 

 and five abdominal somites, and lastly 

 there is the telson (Q. 



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

 of a second buckler, or ' operculum,' covering the abdomen ; 

 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. 



SUB-ORDER 2. EURYPTERIDA. ' Crustacea with numerous, free, 

 thoracico-abdominal segments, the first and second (?) of which 

 bear one or more broad lamellar appendages upon their ventral 

 surface, the remaining segments being devoid of appendages ; 



