C. B. Walcott — Appendages of Trilohites. 24.7 



with Mr. Mitchell and obtained a few specimens for the National 

 Government. 



The most important part of the discovery, announced by Mr. 

 Matthew's paper, is that the Trilobita have true antennas. The dis- 

 covery of the legs and plumose appendages is also of great interest, 

 as it adds to our information respecting the appendages of the 

 Trilobite some of the details of another genus. 



A collection was made for the Yale College Museum by Dr. C. B. 

 Beecher, and in some notes on the thoracic legs of Triarthrus ' 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 CaJymene and Asaplius, and 

 that the exopodite is unlike that of Calymene or Ceraurus. 



Through the courtesy of Prof. J. F. Kemp, of Columbia College, 

 I have examined the material studied by Mr. Matthew ; and Prof. 

 A. H. Chester, of Rutgers College, kindly loaned me for study iive 

 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.^ The limbs of Triarthrus 

 diifer in the details of the joints of the inner branch of the limb 

 (endopodite) and still more in the character of the exopodite. 



Cephalic limbs. — The antennse are uniramose, and, judging from 

 the position in which they are found, were attached to the body near 

 the postero-lateral angle of the hypostoma (Fig. 1, e, PI. VIIL). 

 In one sjDecimen 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 antenna, 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 antennule, it may repre- 

 sent a fifth pair of cephalic limbs. This is also suggested by a 

 section of the limbs within the head of Calymene (illustrated on 

 pi. 1, fig. 9, BulL Mus. Comp. Zool. 1881, vol viii.). In this, a fifth 

 limb is indicated close to the hypostoma. The Trilobite was enrolled 

 so as to include the antennule entirely within the border of the head. 

 A sketch, taken from a photograph of the thin section by transmitted 

 light, is shown by Fig. 8, PI. VllL 



1 Amer. Journ. Sci. 1893, vol. xlvi. pp. 467-470. 



2 The Trilobite ; New and Old Evidence Relating to its Organization. Bull. Mus. 

 Comp. Zool. 1881, vol. viii. p. 6. 



3 Bull. Mus. Comp. Zool. 1881, vol. viii. p. 191-224. Science, 1883, vol. iii. 

 p. 279. 



