722 



ARTHROPODA 



PHYLUM VII 



the central lobe narrow. 



Pio. 1392. 



Lichas laciniatiis Wahlb. 

 Silurian ; Sweden (after 

 Angeliii). 



Corydocephalus 

 Hall and Clarke. 

 New York. 



ptyonurun 

 Silurian ; 



Pygidium small, the pleural lobes crossed by two narrow, 



prominent ribs which end in spines. 

 Ordovician and Silurian ; Europe 

 and North America. 



HoplolicJias Dames (Fig. 1394). 

 Cephalon trilobed, the central lobe 

 produced in front, and not depressed 

 at the back as in Gonolichas. Occipital 

 lobes present. Ordovician to De- 

 vonian ; Europe. 



Geratarges Giirich (Fig. 1395). 

 Glabella with two curved spines in 

 front, and pygidium with numerous 

 spines. Devonian ; Europe. 



Geratolichas Hall and Clarke 

 (Fig. 1396). Cephalon with two 

 pairs of long, curved spines on the 

 axial portion. Devonian ; North 

 America. 



Terataspis Hall. Glabella bulbous, 

 strongly pustulose. Devonian ; North 

 America. 



Fig. 1395. 



Ceratarges armatus 

 (Goldfuss). Devonian ; 

 Germany (after Beyrich). 



Fig. 1394 



Hoploliclias schmidti Dames. 

 Ordovician ; Germany (after 

 Dames). 



Fig. 1396. 



Family 18. Odontopleuridae 

 Burmeister. 



Geratolichas gryps Hall 

 and Clarke. Devonian ; New 

 York (after Hall and Clarke). 



twelve segments. Pygidium small. 

 Ordovician to Devonian. 



Opisnioparia with large free 

 cheeks, small eyes. Thorax of eight to 

 All parts of the crust are usually very spinose. 



In this family, as well as in the Lichadidae, is to 

 be found the highest expression of differentiation and 

 specialisation among the Opisthoparia. The primitive 

 pentamerous lobation of the axis of the cranidium is 

 entirely obscured, and is only clearly seen in the pro- 

 taspis and early nepionic stages. These two families 

 are very closely related, the chief differences being 

 noted in the size and character of the pygidium, and 

 the ribbed or grooved pleura. The Lichades are 

 generally much larger and flatter, but the smaller and 

 spinose forms of Geratarges and Geratolichas approach 

 quite near some of the Acidaspidae. 



Odontopleura Emmrich. Occipital ring smooth or 

 with a median tubercle. Ordovician and Silurian ; 

 EurojDe and America. 



Ascidaspis Murchison (Figs. 1352, 1364, J). 

 Occipital ring with a single median spine. Ordovician 

 and Silurian ; Europe and America. 



Geratocephala Warder (Fig. 1397). Occipital ring 

 with two long, nearly straight, divergent sj)ines. 

 Ordovician and Silurian ; Europe and North America. 



Dicranurus Conrad. Occipital ring with two long spirally recurved 

 Devonian ; Europe and North America. 



Fig. 1397. 



Ceratopephala dufrenoyi (Barr.). Sil- 

 urian (Etage E) ; St. Ivan, BoJiemia 

 (after Barrande). 



spines 



