774 



AETHEOPODA 



PHYLUM VII 



Presfwichia Woodw. (Euproiips Meek; Anthracopeltis Boulay) (Fig. 1499). 

 Differs from Belinurus in having seven coalesced abdominal segments, besides 



a short and obtuse caudal 

 spine. Outline of ab- 

 domen subsemicircular, 

 central axis of body 

 segments narrow. Coal 

 Measures; England, 

 northern France, Russia 

 and Illinois. Type, P. 

 anthrax (Prestw.). 



Protolimuliis Pack. 

 Cephalothorax relatively 

 large, subsemicircular. 



with small appendages ; 



PlfJ. 149S. 



Belinurus reqinae Baily. ^"'- l'*'^^- 



Coal Measures ; Queen's Prestwichia danac (Meek). Coal Meas- . 



County, Ireland. Vi (after ures; MazonCreek,Grundy County, Illinois. itS geiial angles lesS prO- 



Woodward). 2/ (aft,er Packard). ' J j xi, • .r, "1 



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). 



Prolimulns Fritsch. Cephalothorax ellipsoidal, broader than long, without 

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

 shorter than the cephalothorax, with lamellar appendages. Telson slender 

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

 ivoodwardi Fritsch. 



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



(Syn. XiphosuridaG Pocock.) 



Body longer than broad; cephalothorax arched dorsalhj, the central jwrtion 

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

 Abdomen composed of six consolidated segments forming a simple sub-triangidar 

 shield, and a long slender telson. Six p)airs of abdominal limbs, five of them, having 

 over a hundred p)airs of gill-leaves. 



Limulus Miiller, 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 {Ann. 

 Mag. Nat. Hist., 1902, ser. 7, vol. ix.), the foui- 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 

 having the genital opening upon the posterior face. 



The males are smaller than the females, aud are fxirther distinguished by the hooked, not 

 chelate, termination of the second, or second and third appendages, a chai-acter which they 

 acquire only at maturity. The young embryo of Limulus is without an elongated caudal 

 spine, and swims freely by means of its abdominal appendages. With its marked lateral 

 eyes, segmented abdomen and body divided into median and lateral regions by longitudinal 

 grooves, it presents considerable resemblance to a Trilobite, and the stage has in fact been 



