1896. | NEW YORK ACADEMY OF SCIENCES. 245 
Breadth,5 mm. There is considerable variation in the propor- 
tion of the parts. 
“This is an abundant and well-marked species. The pygidium 
is very similar to that of UW. speciosus, Ford, of the Olenellus 
Fauna. In event of the two forms VW. punctatus and MW. pulchel- 
lus proving distinct, I propose that Mr. Hartt’s name, MW. pul- 
chellus, be given to the American species. 
The following particulars may be added to the description of 
this form given by Mr. Walcott, in Bulletin 10. 
The occipital spine is much more slender in the author’s ex- 
amples than in those figured by Mr. Walcott; it is flattened at 
the sides, and frequently rises from the plane of the head shield 
at an angle of 45°. 
The short, transverse furrows on the marginal fold of the 
head shield differ from those of M. Dawsoni in being closer to- 
gether and at about equal distances all around the margin ; they 
are not on the outer surface of the fold. but only indent the 
inner surface of the test, hence they are not visible from above 
when the test is perfect. 
No complete thorax has been found in connection with the 
shields, but the separated joints show a strong axial ring which 
has a row of obscure tubercles along the ridge similar to those 
on the posterior rings of the rachis; the pleure are strongly 
arched, and have a long and deep furrow directed somewhat 
obliquely backward ; they seem not very rigid and terminate in 
rounded points. 
According to Mr. Walcott the median lobe of the pygidium 
has eight segments, including the articulating ring, but well 
grown examples show nine well marked rings, and three other 
smaller, less distinct ones, near the end of the rachis. When 
one-quarter grown this species has seven distinct rings in the 
rachis, the number in the mature M. punctatus, according to Mr. 
Salter. From this species M. pulchellus differs not only in re- 
spect to the number of these rings, but also in having a smaller 
and more erect occipital spine. 
Sculpture.—The test of M. pulchellus has been described as 
punctate, but this remark applies only to the head shield and 
thorax, for the pygidium is tuberculate on the side lobes. It 
may be added that the strong rings of the rachis carry each a 
low spine at the summit; but on the weak posterior rings the 
crest is ornamented with a row of small tubercles. 
Size.—The dimensions given above are of the largest shields, 
more frequently it is a third smaller. 
Development of the Young.—The change of this species as it 
grew from a Protaspis stage similar to that of other trilobites 
