96 Walcott Appendages of the Trilobites. 



Description of Plate. 



Fig. 1. Triarthrus becki (X3). Outline of carapace, with appendages rep 

 resented as they occur on several specimens, their relative 

 position being retained. 



a, a, a, a. Endopodites of limbs showing variation in joints. 



b, b. Plumose portion of exopodite. 



c, c. The outer or supporting portion of the setae or fimbriae 



of b, b. 



d, Limbs extending from beneath the pygidium, showing large 



proximal joints. Those of the left side are imperfectly 

 preserved. 



e, Antenna extending back nearly to the postero-lateral margin 



of the hypostoma. 

 /. One of the cephalic limbs. The basal joint may be broken 



away on the inner side. 

 g. Cephalic limb. 



Fig. 2 (X7). Limbs attached to the under surface of an individual preserv 

 ing 13 thoracic segments and the pygidium. The limbs (a to 

 k) on the left side are mainly in place. A fracture cuts out 

 one limb between g and h. 



a to g. Limbs preserving traces of the enlarged proximal joints. 



b, d. Limbs preserving the two joints of the protopodite and two 

 of the large proximal joints. 



I, m, o. Exopodites, showing under or side views. 



n. Enlargement of fimbrise of m. 



r, s. Distal joints of endopodites of right side. 



y. Portion of an exopodite showing its inner support. 



Fig. 3. Limbs occurring on the under side of an individual of 14 thoracic 



segments, 

 a, b, c, d. Limbs with flattened, enlarged proximal joints and 



slender distal joints. 



a. Limb preserving large joint of protopodite, four enlarged prox 

 imal joints and three slender distal joints. At x the point 

 of attachment of an exopodite is shown, and in the speci 

 men it looks as though / had been broken away from x. 



Fig. 4. Restoration of the thoracic limbs of the fifth segment anterior to 

 the pygidium. 



en. endopodite. p. protopodite. a. four proximal swimming 



joints, b. three distal joints. 

 ex. exopodite, attached to same joint of the protopodite as the 



endopodite. 



