198 PALEONTOLOGY 



entire. The pygidial pleura are covered with little 

 tubercles. 



Very little is known of the limbs of Calymene : traces 

 of 'them have been found in sections of enrolled specimens, 

 including spiral structures which are probably gills 

 carried on the limbs. 



2. Dalmanites caudatus (often called Phacops cau- 

 datus) is another famous Dudley trilobite (Fig. 56). The 

 most important differences between it and Calymene are 

 these : The marginal rim of the head-shield is drawn out 

 into a slight point in front and into a pair of genal spines 

 behind. The glabella is much wider in front, instead of 

 narrower ; its lateral furrows are nearly straight and do 

 not mark off rounded lobes as in Calymene, but converge 

 towards the middle line, leaving a much narrower smooth 

 central area. The eyes are very large, usually well- 

 preserved, and the compound character is obvious, the 

 surface being divided into a large number of corneal 

 facets arranged in a very regular manner. The facial 

 suture is very distinctly proparian, cutting the lateral 

 margin some way in front of the genal angle and making 

 a right-angled bend at the eye ; in front it runs round 

 the front margin of the glabella from one side to the 

 other, not cutting the front margin of the head-shield, 

 so that the two free cheeks form one inseparable piece. 

 The labrum is somewhat triangular (Fig. 61, d). 



The thorax consists of eleven somites, which differ 

 from those of Calymene chiefly in the relative narrow- 

 ness of the axis (about one-quarter the total width, 

 instead of nearly one-third). 



