I 5 8 



THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



triangular in shape, with the point backward, but in all the endopodites at the anterior end 

 of the thorax, the triangle has a very obtuse angle at the apex, and the base is much longer 

 than the perpendicular. On the other hand, those of the pygidium, which were figured by 

 Beecher, have a number of short wide segments, all wider than long, and, excepting the 

 dactylopodites, triangular in form. 



Measurements: Length, 8.75 mm. ; width at back of cephalon, about 4 mm. 



Specimen No. 230 (pi. 5, fig. 3; text fig. 44). 

 Illustrated: Amer. Jour. Sci., vol. 47, 1894, pi. 7, fig. 2 (drawing); Ibid., vol. 13, 1902, pi. 2, fig. 2. 



An entire specimen of medium size, developed from the ventral side. It seems to have 

 been the first one to yield to Professor Beecher any satisfactory knowledge of the appen- 



Fig. 44. Triarthrus becki Green. Appendages of the posterior 

 part of the thorax and pygidium of specimen 230. Inked by Miss 

 Wood from a tracing made under the direction of Professor Beecher. 



dages of the pygidium. There are five endopodites, all on one side, which appear to belong 

 here. The segments in this region are characterized by their short, wide, triangular form. 

 At the apex of each is a small tuft of spines or short hairs, and the ventral surfaces of some 

 of the endopodites show pits for the insertion of spines. 



Measurements: Length, 21 mm.; width at back of cephalon, 10 mm. 



CRYPTOLITHUS TESSELLATUS GREEN. 

 Specimen No. 233 (pi. 7, fig. i; text fig. 45). 



This is the best preserved entire specimen. It is developed from the lower side, and 

 shows the hypostoma, antennules, and a few fragmentary appendages of the cephalon, the 

 outer portions of the exopodites of thorax and pygidium on both sides, and the endopodites 

 on the left side. 



The hypostoma is imperfectly preserved and is turned completely around, so that the 

 anterior margin is directed backward, and the posterior one is so much in the shadow that 

 it does not show well in any of the photographs. The form is, however, essentially like 



