672 



ARTHROPODA 



SUB-KINGDOM VII 



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



Body longer than broad; cephalothorax arched dorsally, the central portion separated 

 from the sides by 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- 



Limulus, Miiller (Fig. 1413). Living species belonging to this, the only genus of 

 the family, occur on the eastern shores of America and Asia. The four cephalothoracic 

 feet are chelate, the sixth pair 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. A small species of Limulus occurs in the Buntersandstein of the 

 Vosges. L. Walchi is abundant in the Lithographic Slates of Bavaria ; L. Decheni is 

 found in the Oligocene brown coal of Teuchern, near Merseburg. 



Order 2. SYNXIPHOSURA. Packard. 



Body elongated ; cephalothorax semicircular with the median portion more or less 

 distinctly defined. Compound eyes present in some forms, ocelli not observed except in 

 Neolimulus. Abdomen distinctly trilobed, its segments free, the 

 pleurae fiat and extended, and (except in Bunodes) terminating in 

 lateral projections or 



A las ns'satoni wiutf 

 ria 



3/j. 



With the exception of the Cambrian Aglaspis, all the genera be- 

 longing to this order are of Silurian age, and are too imperfectly 

 known as yet to permit a satisfactory grouping into families, although 

 several such have been proposed by Packard. Zittel united them, 

 together with certain genera of Xiphosura, in the family Hernia spidae, 

 and this term is retained with the exclusion of the Xiphosurous forms 

 and Aglaspis. The latter is without facial sutures. 



Family 1. Aglaspidae. Clarke. 



Cephalothorax moderately large, trilobed; abdominal segments 

 Upper Cambrian; Lodi, with distinct axis and pleurae ; telson long, spiniform. 



Wisconsin. 3/j. 



Aglaspis, Hall (Fig. 1414). Cephalothorax with central 

 portion short and conate, in front of which are approximate com- 

 pound eyes ; bounded on all sides by a distinct border. Abdominal 

 segments not grooved on the pleurae. Cambrian ; Wisconsin. 



Family 2. Hemiaspidae. Zittel. 



A somewhat heterogeneous group, separated by at least a 

 family difference from the Aglaspidae. 



Neolimulus, Woodw. Cephalothorax short and broad, crescentic, 

 elevated mesially, and bearing ocelli. Compound eyes lateral, and 

 connected with the genal angles by a snture. Abdomen very 

 broad, composed of at least nine trilobed segments ; telson not 

 observed. This genus connects the Xiphosura with the Synxi- 

 phosura. Silurian ; Scotland. 



Bunodes, Eichw. (Exapinurus, Nieszk.), (Fig. 1415). Cephalo- ten; Robtzikuii, pesei. 



v T . ' Tin f -, -,. Posterior segments re- 



thorax semicircular, convex, with radial furrows from the median stored from another 

 portion. Eyes wanting, and no genal spines. Facial sutures gj^midt) 611 (af1 

 obscure, converging from the posterior to the anterior margin. 

 Abdomen divided into an anterior portion (" thorax ") consisting of six trilobite-like 



FIG. 1415. 



l;<i amirs lunula, var. 

 SdirenJd, Xieszk. Silur- 



