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). 



