10 
SILURIAN 
8- CALYMENE NIVALIS- 
Plate 1 , figs. 24-20. 
C. sesqui-uncialis ; capite subtrigono ; cauda rhomboidea con- 
vexa ; abdomen deest. Glabella parabolica, brevis, longitudinem 
i-capitis sequans ; lobis duobus basalibus intervallo lato separatis ; 
tertio minuto. Margo anticus latus rotundus, a genis vallo lato 
sejunctus. Oculi eminentes. Cauda convexissima elongata, axi antice 
lato, postice contracto, lateribus parallelis, apice abrupta. Axis sulcis 
circiter 8-propinquis ; latera 6-costata, costis ad marginem attingenti- 
bus, duplicatis. Labrum angustum, oblongum, sulcis duobus concen- 
tricis, apice bilobato. 
The species is near to several European ones, yet distinct 
from all. It has the short glabella and prominent eyes of C. 
brevicapitata, and is even more gibbous than that species. 
The tail lias a remarkably produced convex tip, like that of 
C. Tristani, which has, however, fewer ribs, more deeply inter¬ 
lined. 
About 1^ inch long, with a subtriangular head and rhom- 
boidal convex tail. We have no body segments. 
The glabella is convex, parabolic, short—only measuring 
half the entire length of the head, with the usual three lateral 
lobes, the basal ones more than their own width apart; and 
the other one minute. The front margin broad, rounded, 
separated by broad depressions from the cheeks. Eyes very 
prominent, opposite the middle glabella lobe. The tail is very 
convex; the axis is broad in front, tapers backwards to about 
the half, and thence is parallel-sided to the end of the promi¬ 
nent blunt tip. The axis is closely scored half-way down by 
eight or nine ribs; the declining lateral lobes have six stout 
ribs, which reach the extreme margin, and are duplicate for 
a short distance from the edge. 
The labrum (wrongly called hypostome by many authors) is 
narrow-oblong, with two concentric furrows and a bilobed tip. 
This genus, had no other been found, would have marked the 
beds in which it occurs as Silurian, for it begins at the Silurian 
