neolenus. 2 i 
The Appendages of Neolenus. 
historical. 
The first mention of Neolenus with appendages preserved was in Doctor Walcott's 
paper of 191 1, 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. 701). 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, 191 1, p. 20, pi. 6, figs. 1, 2 (exopodites of thorax and 
cephalon) ; — Ibid., vol. 57, 1912, p. 191, pi. 24, figs. 1, ia (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. 1; 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 
