NEOLENUS. 2 1 



THE APPENDAGES OF NEOLENUS. 

 HISTORICAL. 



The first mention of Neolenus with appendages preserved was in Doctor Walcott's 

 paper of 1911, in which two figures were given to show the form of the exopodites in com- 

 parison with the branchiae of the eurypterid-like Sidneyia. In 1912, two more figures were 

 presented, showing the antennules, exopodites, and cerci. The specimens were found in the 

 Burgess shale (Middle Cambrian) near Field, in British Columbia. This shale is exceedingly 

 fine-grained, and has yielded a very large fauna of beautifully preserved fossils, either 

 unknown or extraordinarily rare elsewhere. It was stated in this paper (1912 A) that 

 trilobites, with the exception of Agnostus and Microdiscus, were not abundant in the shale. 



In discussing the origin of the tracks known as Protichnites, Walcott presented four 

 figures of Neolenus with appendages, and described the three clawlike spines at the tip of 

 each endopodite. 



Three new figures of the appendages were also contributed to the second edition of the 

 Eastman-Zittel "Text-book of Paleontology" (1913, p. /oi). Later (1916, pi. 9) there 

 was published a photograph of a wonderful slab, bearing on its surface numerous Middle 

 Cambrian Crustacea. Several of the specimens of Neolenus showed appendages. 



Finally, in 1918, appeared the "Appendages of Trilobites," in which the limbs of 

 Neolenus were fully described and figured (p. 126), and a restoration presented. Organs 

 previously unknown in trilobites, epipodites and exites, attached to the coxopodites, were 

 found. 



Neolenus serratus (Rominger). 

 (Text fig. 2-8.) 



Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1911, p. 20, pi. 6, figs. I, 2 (exopodites of thorax and 

 cephalon) ; Ibid., vol. 57, 1912, p. 191, pi. 24, figs, i, la (antennules, caudal rami, and endopodites of 

 thorax) ; Ibid., vol. 57, 1912, p. 277, pi. 45, figs. 1-4 (antennules, endopodites of cephalon and thorax, caudal 

 rami) ; Text-book of Paleontology, edited by C. R. Eastman, 2d ed., vol. i, 1913, p. 701, fig. 1343 (exopo- 

 dites), p. 716, fig. 1376 (abdominal appendages), fig. 1377 (appendages of thorax and pygidium) ; Ann. 

 Rept. Smithson. Inst. for 1915, 1916, pi. 9; Smithson. Misc. Coll., vol. 67, 1918, pp. 126-131 et al., pi. 14, 

 fig. i; pis. 15-20; pi. 21, fig..6; pis. 22, 23; pi. 31 (restoration); pi. 34, fig. 3 (restored section); pi. 35, 

 fig. 4; pi. 36, fig. 3 (hypostoma). 



The following description of the appendages of Neolenus is summarized from Walcott's 

 paper of 1918, and from a study of the eight specimens mentioned below. 



Cephalon. 



The antennules are long, slender, and flexible, and lack the formal double curvature so 

 characteristic of those of Triarthrus. There are short fine spines on the distal rims of the 

 segments of the proximal half of each, thus giving great sensitiveness to these organs. In 

 the proximal portion of each, the individual segments are short and wider than long, and in 

 the distal region they are narrow and longer than wide. 



There are four pairs of biramous cephalic appendages, which differ only very slightly 

 from the appendages of the thorax. All are of course excessively flattened, and they are here 

 described as they appear. 



The coxopodites, shown for the first time in Walcott's paper of 1918, are broad, longer 

 than wide, and truncated on the inner ends, where they bear short, stout, unequal spines 



