1850.] FLETCHER ON DUDLEY TRILOBITES. 405 



and gibbous in front, and its border of tubercles less distinct ; while 

 the posterior angles of the cephalic shield are obtuse, and not pro- 

 duced into spines ; each angle is ornamented with a cluster of tuber- 

 cles, and occasionally terminates in a single large tubercle. 



The tail is convex and triangular, its length and breadth about 

 equal, and its axis of ten rings much narrower than its lateral por- 

 tions, and gradually diminishing to its blunt apex. Seven broad ribs 

 on each side are strongly arched downwards, and bent backwards ; 

 the posterior ribs are rounded off at their extremities, and extend 

 below the blunted axal termination. Each lateral rib has a tubercle 

 at its origin. 



The upper ring of the axis has usually a single large tubercle upon 

 its centre ; the second has a central punctum or slight depression be- 

 tween two large tubercles ; the remaining rings having alternately a 

 tubercle and a punctum between two tubercles, except the three pos- 

 terior rings, which have each a single tubercle only. 



Varieties. — The front of the glabella is more gibbous in some spe- 

 cimens than in others, and the markings upon the tail are not quite 

 constant. 



EXPLANATION OF THE PLATE. 



Figs. 1, 4, 6, 9 and 10 are from the rich cabinet of ray friend Mr. John Gray of 

 Dudley ; 7 and 8 from the collection of Mr. Charles Twaraley, to whom I am in- 

 debted for their use ; and the remaining specimens are from my own collection. 

 Fig. 1. Cyhele punctata, full-grown. 

 Fig. 1 a. The same specimen, under side of the head showing the hypostome, and 



the tubercle against which it abuts. 

 Fig. 1 b. The eye, magnified, upper side. 

 Fig. 1 c. Ditto, ditto, lower side. 

 Fig. 1 d. The tenth thoracic segment with its spine. 

 Fig. 2. The same species, adult specimen. 

 Fig. 3. Ditto, the tail. 

 Fig. 4. Ditto, the under side of the thorax and tail, to show the bifid or notched 



terminations of the pleurae, and the manner in which they are applied to 



each other in rolling up. 

 Fig. 5. Ditto, the hypostome ; the hooded tip is slightly recurved. 

 Fig. 6. Cyhele variolaris, young specimen. 

 Fig. 7. Ditto, rolled up. 

 Fig. 8. Ditto, nearly full-grown. 

 Fig. 8 a. Ditto, a side view of same specimen. 

 Fig. 9. Ditto, a fine specimen ; the thorax is slightly bent backwards ; it shows the 



sharpened front edges and notched terminations of the pleurae. 

 Fig. 9 a. Ditto, the under side of the head of the same specimen ; the hypostome is 



not recurved at the tip, but regularly convex. 

 Fig. 9 b. Ditto, a few of the tubercles with a punctum on each, as mentioned by 



Brongniart. 

 Fig. 10. Ditto, an under view, showing a similar structure to that represented at 



fig. 4. 



