722 



ARTHROPODA 



PHYLÜM VII 



tlie central lobe narrow. 



Fia. 1392. 



Lii-Iins laciniatus 

 Siluriaii ; Sweden 

 Angeliii). 



Wahlb. 

 (after 



13! »3. 



Corydocephul us pti/onurufi 

 Hall and Clarke. Silurian ; 

 New York. 



Pygidium small, tlie pleural lobes crossed by two narrow, 

 prominent ribs which end in spines. 

 Ordovician and Silurian ; Europe 

 and Nortli America. 



Hoplolichas Dames (Fig. 1394). 

 Ceplialon trilobed, the central lobe 

 produced in front, and not depressed 

 at the back as in GonoUchas. Occipital 

 lobes present. Ordovician to De- 

 vonian ; Europe. 



Geratarges Gürich (Fig. 1395). 

 Glabella witli two curved spines in 

 front, and pygidium with numerous 

 spines. Devonian ; Europe. 



Geratolichas Hall and Clarke 

 (Fig. 1396). Ceplialon 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). 



Fio, 1394, 



Hoplolichas schmidti Dames. 

 Ordovician ; Germany (after 

 Dames). 



Fig. 1396. 



Geratolichas gryps Hall 

 and Clarke. Devonian ; New 

 York (after Hall and Clarke). 



Family 18. Odontopleuridae 

 Burmeister. 



twelve Segments. Pygidium small. 

 Ordovician to Devonian. 



Opisthoparia lüith large free 

 cheeks, small eyes. Thorax of eight to 

 All parts of the crust are usually very spinöse. 



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 m 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 

 spmose 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- 

 Europe 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 spines 

 Ordovician and Silurian ; Europe and North America 



Fig. 1397. 



Geratocephala dufrenoyi (Barr. ). Sil- 

 urian (Etage E) ; St. Ivan, Bohemia 

 (after Barrande). 



I 



