ORDOVICIAN FAUNAS. 203 
out. Among the specimens of pygidia which have been observed there 
are some which are smaller and proportionately much broader, with 
a smaller number of segments both on the axis and on the plure. 
The axial segments of these smaller specimens are intermittently tu- 
bercular as in the larger ones, and it is believed that they are only 
immature individuals of the same species. 
The original L. trentonensis, which was described from Wisconsin 
and Ilhnois, has never been illustrated, but the New Jersey specimens 
agree in general very closely with the description of the species. There 
is some difference in the arrangement of the tubercular segments of 
the axis, but the New Jersey specimens exhibit some variation in this 
respect among themselves; the important character seems to be the 
intermittence of the tubercular segments, and not the exact position 
of these segments. 
The species is a close analog of H. serbacht Schm.* from Russia. 
CALYMENE SENARIA Con. 
Plate XV., Fig. 28. 
1847. Calymene senaria Hall, Pal: N. Y., vol. I., p. 238, pl. 64, figs. 
3 a—N. 
Description.—Head sub-semi-cireular or sublunate in outline, the 
anterior and lateral margins being more or less nearly regularly 
rounded, and the posterior broadly sinuous, with the posterior lateral 
extremities bluntly subangular or abruptly rounded. Free cheeks 
irregularly triangular in outline, with thick, rounded, lateral mar- 
gins, defined by a distinct, rounded, marginal furrow, which is con- 
tinuous with the furrow separating the anterior end of the glabella 
from the prominent, elevated, anterior margin of the head. Facial 
sutures originating just in front of the genal angles, passing obliquely 
forward and inward for a little more than half the distance to the 
eyes, then curving inward to the base of the eye-lobe, and, after pass- 
ing around the eyes, extending forward and intersecting the anterior 
margin at points a little nearer together than the breadth between 
the eyes. Eyes small and rather prominent. Glabella more promi- 
nent than the cheeks and separated from them by deep, dorsal fur- 
* Rev. Ostbalt. Sil. Tril., pt. I., p. 229. 
