NIAGARA GROUP. 
101 
1. Asaphus limulurus (Green, Monograph , p. 48.) — This fossil is known by the great 
length of the caudal extremity, which is often produced nearly an inch beyond the articula¬ 
tions. The form figured is the most common, and will be recognized as the most abundant 
of the Trilobites at Lockport. 
This species is remarkably similar in many particulars to the A. longicaudatus of Murchi¬ 
son, but differs from it in the shorter tail and the greater width at its base, being much less 
slender. It has also fewer articulations in the post abdomen, ten or eleven being the extreme 
number. With these exceptions, our fossil is very similar to the English one, and apparently 
holds the same place in the series, eminently characterizing the lower part of the Niagara 
group as that does of the Wenlock; these formations of the two countries being equivalent, 
so far as we are able to decide. 
2. Head of Asaphus limulurus. — The head of this species being so abundant at Rochester 
and other places in Monroe county, where perfect specimens are rare in the ordinary expo¬ 
sures of the rock, that it seemed desirable to present it as it there occurs. The eyes are 
usually detached, their form only being perceptible. The anterior portion of the buckler is 
produced in a blunt point, its posterior angles extending backward and terminating in acute 
points, which, in perfect specimens, reach to the fifth rib of the abdomen. Each side of the 
middle lobe of the head is marked by three indentations or furrows, the anterior one extending 
obliquely forward. 
