774 



ARTHROPODA 



PHYLÜM VII 



PrestwicUa Woodw. {Euproöps Meek ; Jnthracopeltis Boulay) (Fig. 1499). 

 Differs from Belinurus in having seven coalesced abdominal segments, besides 



a shortand obtuse caudal 

 spine. Outline of ab- 

 domen subsemicircular, 

 central axis of body 

 Segments narrow. Goal 

 Measures; England, 

 northern France, Russia 

 and Illinois. Type, F. 

 anthrax (Prestw.). 



Protolimulus Pack. 

 Cephalothorax relatively 

 large, subsemicircular, 

 with small appendages ; 

 its genal angles less pro- 

 duced than in the two 

 preceding genera. Abdomen with six segments besides a large, thick caudal 

 spine. Upper Devonian (Chemung Group); Pennsylvania. Type, Prot, 

 eriensis (Williams). 



Prolimulus Fritsch. Cephalothorax ellipsoidal, broader than long, without 

 genal angles, and with relatfively long appendages. Abdomen rounded, 

 shorter than the cephalothorax, with lamellar appendages. Telson slender 

 equalling one-half the total body length. Permian ; Bohemia. Type, P. 

 woodwardi Fritsch. 



Fio. 1408. 



Belinurus reqinae Baily. 

 Goal Measures ; Queen's 

 Couiity, Ireland. Vi (aft«r 

 Woof] ward). 



Fia, 1499. 



Goal Meas- 



Prestwichia danae (Meek). 

 nres; MazoiiCreek,Grundy County, Illinois. 

 2/3 (after Packard). 



Family 3. Limulidae Zittel (King or Horseslioe Crabs). 

 (Syn. Xiphosuridae Pocock.) 



Body lov.ger than hroad ; cephalothorax arched dorsally, the central portion 

 separated from the sides hy longitudinal grooves ; marginal area large and flat. 

 Abdomen composed of six Consolidated segments forming a simple sub-triangular 

 shield, and a long slender telson. Six pairs of abdominal limbs, five of them having 

 over a hundred pairs of gill-leaves. 



imwZws Müller, restricted by Fabricius (Fig. 1500). Living species belong- 

 ing to this, the solitary genus of the family, occur on the eastern shores of North 

 and Central America and Asia. According to Pocock's Classification {Jnn. 

 Mag. Nat. Hist., 1902, ser. 7, vol. ix.), the four Asiatic species are referable 

 to two genera distinct from Limulus s.s. In all forms the four cephalothoracic 

 feet are chelate, the sixth pair is furnished with a whorl of plates used in 

 pushing the animal through the mud. Gills are borne upon the five posterior 

 pairs of abdominal appendages, the anterior pair being without gills, but 

 havmg the genital opening upon the posterior face. 



ohJJt^ males are smaller than the females, aud are further distinguished by the hooked, not 

 Ron n-r!' ^^^"^'"^^^«^ of the second, or second and third appendages, a cliaracter which they 

 «n?np l.^ ^ *• "^f "^jty- The young embryo of Limulus is without an elongated caudal 

 eSo^ C",,,lTT'/r'^^ ^y ?^.^'\^ ^^ '^^ abdominal appendages. With its mSrked lateral 

 Svp^" f^ abdonien and body divided into median and lateral regions by longitudinal 

 grooves, it presents considerable reseinblance to a Trilobite, and the stage has in ttct been 



