90 Walcott — Appendages of the Trilohites. 



C. E. Beecher, and in some notes on the thoracic legs of Tri- 

 arthrus* he describes and illustrates a dorsal view of the legs of 

 the second and third free thoracic segments. These show that 

 the endopodite of the leg is essentially the same as in Calymene 

 and Asaphns, and that the exopodite is unlike that of Calymene 

 or Ceraurus. 



Through the courtesy of Prof. J. F. Kemp of Columbia Col- 

 lege, I have examined the material studied by Mr. Matthew; 

 and Prof. A. H. Chester, of Eutgers College, kindly loaned me 

 for study five specimens that he purchased from Mr. Valiant. 

 From these and the specimens in the National Museum a few 

 notes have been taken that permit of some comparisons with the 

 extremities found in Ceraurus, Calymene and Asaphus.f The 

 limbs of Triarthrus differ in the details of the joints of the in- 

 ner branch of the limb (endopodite) and still more in the char- 

 acter of the exopodite. 



Cephalic limbs.— The antenna3 are uuiramose, and, judging 

 from the i^osition in which they are found, were attached to the 

 body near the postero-lateral angle of the hypostoma (Fig. 1, e, 

 Plate 1). In one specimen a cephalic limb somewhat detached 

 from its true position shows a large basal joint and six slender 

 joints (Fig. 1,/). The basal joint does not show conclusive 

 evidence of the presence of a masticatory ridge. On another 

 specimen, however, the form of the basal joint strongly suggests 

 that it subserves the purpose of mastication. This is illustrated 

 at g in Fig. 1. 



A slender jointed appendage like that attached to the basal 

 joint of g occurs between it and the antennae and is probably a 

 portion of another one of the cephalic limbs. No other cephalic 

 appendages have been observed in the material at hand. 



Since the publication of my articles on The Trilobite| I found 

 in a section of the head of Calymene senaria a slender jointed 

 limb that appears to have been an antennule. It is unlike any 

 limb found beneath the head and thorax, and, if not an anten- 

 nule, it may represent a fifth pair of cephalic limbs. This is 



*Am. Jour. Sci., Vol. 46, 1893, pp. 467-470. 



tThe Trilobite ; New and Old Evidence Relating to its Organization. 

 Bull. Mus. Couip. Zool., Vol. 8, 1881, p. 6. 



JBull. Mus. Comp. Zool., Vol. 8, 1881, p. 191-224. Science, Vol. 3, 1883, 

 p, 279. 



