80 
AUG. F. FOERSTE 
ville but also at the Moody quarry, in the southeastern part of 
Wilmington, Ohio, from which specimens occur in the collection 
of T3r. George M. Austin. The pygidium, in the best preserved 
interior cast found in this collection, figured herewith, has 7 
pairs of ribs, of which the last pair is very short and is indicated 
chiefly by the nodular elevation of part of this rib. A cast of 
the exterior of another specimen suggests the possibility of an 
eighth pair of ribs, but this is doubtful. The chief character- 
istic of the species, as far as known, is found in the curvature of 
the ribs. The axial lobe is almost straight from front to rear. 
From this lobe all of the anterior ribs diverge strongly, and 
the backward curvature of their distal halves is more moderate 
than in any other Silurian species. The posterior termination 
of the pygidium of this species is unknown. 
In Encrinurus reflexus Raymond (Bull. Mus. Comp. ZooL, 
60, 1916, p. 25, pi. 3, figs. 7, 8) from the Niagaran at Wauwatosa, 
Wisconsin, there are 8 pairs of ribs, and these are deflected more 
strongly toward the rear. 
Encrinurus hillsboroensis sp. nov. 
Encrinurus cf. ornatus, Ohio Jour. Sci., 1919, p. 391, pi. 18, figs. 2 A-C. 
In the Holophragma zone, at the top of the West Union for- 
mation, at Hillsboro, Ohio, fragments of a species of Encrinurus 
occur which differ from either Encrinurus ornatus^ or Encrinurus 
reflexus in the strong posterior reflexion of the distal parts of the 
ribs on the pygidium. There are 8 pairs of ribs and the pygidium 
terminates posteriorly in an acute spinose end. It is probable 
that a similar termination would be found also on the pygidia of 
other species if these parts were preserved. 
In Encrinurus thresheri Foerste (Bull. Sci. Lab. Denison Univ., 
2, 1887, p. 101, pi. 8, fig. 26; also pL XVIII, fig. 10 of present 
issue) the ribs curve strongly backward as in Encrinurus hills- 
horoensis, but there are only 6 pairs of distinctly defined ribs, 
with a doubtful seventh pair parallel to the posterior end of the 
axial lobe. The type apparently is a cast of the lower surface 
of the pygidium, which accounts for the apparent narrowness of 
the ribs. 
