TRILOBITES. 743 
Cybele winchelli.] 
one-fourth the width of the thorax at any point. The segments are slender 
and distinctly grooved for their entire length or within a very short distance of 
their extremities. The first five segments appear to be obtusely rounded at 
their terminations, but the last seven are acute. The sixth segment, though no 
broader than the rest within the articulating lines, is greatly expanded at the 
line of geniculation and each extremity is produced as a stout spine, “consider- 
ably beyond the termination of the pygidium; these curve outward at first, 
thence recurve and approach each other. Though their entire length is not 
preserved, they could not have been less than 20 mm. long. The last six segments 
are like the first five, except that they are curved more abruptly backward, their 
terminations being acute. 
Pygidium short, narrow in front, all the annulations being curved abruptly 
backward. Anterior diameter 7.5 mm.; length 9 mm. The articulating ring of the 
axis is very large and conspicuous; behind it is a single annulation extending entirely 
across the axis, three others which extend from the dorsal furrows partly across, 
these being followed by five or six rings which do not reach the dorsal furrows and 
are separated medially by a flattened area, like that in Encrinurus. The axis ends 
acutely and does not reach the extremity of the pygidium. 
Each of the pleurz bears four or five ribs, the first of which is quite narrow, and 
is, probably, the anterior moiety of the second, as it does not reach the margin. 
There may also be seen a trace of a similar intercalary rib between the second and 
third ribs. The second, third, fourth and fifth ribs end in acute, free points which 
were directed outwardly. 
Surface finely tubercled, the tubercles being coarsest on the border of the 
cephalon and the ribs of the pygidium. The surface of the free cheeks was slightly 
pitted or punctated. 
Formation and locality—Galena limestone (?), Fillmore county, Minnesota (Museum No. 8435). This 
specimen was found loose, and its exact geological position is, hence, uncertain. 
Observations—This is the most completely known species of Cybel’ from the American faunas, 
indeed the only species of the genus observed here except that figured by Billings under the name En- 
crinurus mirus, from the Quebec group of Newfoundland;* and of all the forms of this genus that have 
been illustrated no specimen shows better the general form and relation of the parts. 
Cybele is an eminently lower Silurian genus, attaining its maximum development and variation of 
form in the Scandinavian and Baltic Silurian districts, at an horizun equivalent to that of C. winchelli. 
The unfortunate condition of the glabella of our specimen precludes a thoroughly reliable comparison 
with other forms; but the character of its pygidium, with short free terminations of the ribs, suggests a 
specific relationship with C. revalensis Schmidt,{ from the ¢tage C,, a somewhat earlier stage of the Tren- 
ton period than that represented by the Galena limestone. None of the Russian species possess the long 
cheek spines of C. winchelli. 
* Paleozoic Fossils, vol. i, p. 292, fig. 282, 1865. The species was founded on a glabella, which is suspiciously like that of 
Amphion; the pygidium, however, associated with it in the illustration but not in the description, is probably that of a 
Cybele. 
+ Revision der ostbalt. silur. Trilobiten, Abth.1, p. 207, pl. xtrt, fig. 20; pl. xv, figs. 6, 7; pl. xvi. fig. 40. 
