36 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
CHEIRURUS DILATATUS, Sp. nov. 
Plate 4, fig. 1, 3. 
Sphaerexochus romingeri ? Hall, 28th Rept. N. Y. state mus. nat. hist., 1877, 
doc. ed., pl. 32, f. 16. 
Ceraurus (Cheirurus) niagarensis Hall, 28th Rept. N. Y. state mus. nat. hist., 
1879, mus. ed., p. 189, pl. 32, f. 16; 11th Ann. rept. Dept. geol. and nat. 
hist. Indiana, 1882, p. 335, pl. 34, f. 16, non pl. 33, f. 10. 
In the discussion of Cheirurus niagarensis (p. 30) frequent mention 
has been made of the pygidium from Waldron which Hall figured. 
This pygidium differs radically from the pygidia which have been 
referred to Ch. niagarensis and Ch. welleri, in having broad, short 
spines, each marked by a depressed line. This appearance of the 
spines is probably due to crushing, in so far as the depressed line is 
concerned, but the spines are decidedly shorter and broader than 
those of the species previously described. 
Cheirurids seem to be rare at Waldron for a search through an ex- 
tensive collection from that locality in the M. C. Z. has revealed only 
one good cranidium, one poor one, and a pygidium. The best speci- 
men is a fairly well-preserved cranidium, having much the general 
appearance of Ch. niagarensis, only larger. On a closer examination 
of the proportions, however, it is seen that this form is longer and 
narrower than the typical specimens of Ch. niagarensis, and the 
glabella makes up a larger proportion of the cephalon. In a specimen 
of Ch. niagarensis from Rochester (M. C. Z. 625) the length is .57 of 
the width and in the specimen from Waldron (M. C. Z. 628) it is .67. 
In the first species the width of the frontal lobe of the glabella is less 
than half the width of the cephalon (.46). In the latter specimen it 
is somewhat more (.60). These appear, in figures, relatively small 
differences, but when the areas involved are compared it is at once 
seen that the glabella of the Waldron specimen is much larger than 
that of the specimens of Ch. niagarensis. 
It is of course uncertain whether the pygidium described by Hall 
is to be associated with the cranidium here discussed. It may belong 
to the same species, and they are provisionally associated. The 
cranidium is, however, made the holotype of the species, and the 
pygidium a paratype. 
A large Cheirurus. The cranidium is dominated by the glabella, 
whose frontal lobe is more than one half as wide as the total width 
