1870. ] _ BILLINGS —LOWER-SILURIAN TRILOBITES. 485 
2. No fossils of the order (Xiphosura) to which Limulus belongs 
have been found so low down as the Potsdam sandstone. 
3. Large Trilobites occur there in abundance. 
The weight of the evidence, therefore, favours the opinion that 
the tracks in question are those of Trilobites. It is important to 
bear in mind that Protichnites and Climactichnites occur together on 
the same slabs of sandstone. Dr. Dawson’s observations clearly 
prove that both might have been made by an animal of the same 
species under different circumstances, accordingly as its walking- or 
its swimming-feet were made use of. Judging from the width of 
the tracks, I believe that several of those of both kinds on one of the 
slabs, now in the Museum of the Survey, were made by the same 
individual. 
4, Ona rolled- up specimen of Calymene senaria filled with small 
ovate bodies. 
Tt is above stated that while seeking for additional evidence re- 
lating to the limbs of Trilobites, a number of specimens were cut up 
and polished, One of these was an exceedingly perfect, rolled-up 
Calymene senaria, from the Hudson-River group at Cincinnati, in 
Ohio. 
This animal*(Pl. XXXII. fig. 3) appears to have shut itself up so 
completely that the fine mud in which it was buried could only 
gain access through the small fissure at a, where the points of the 
head and tail come together. There is here a small space, within 
the letters, c, d, ¢, f, which is of a light yellowish brown. I think 
that neither the mud, nor even the muddy water, penetrated fur- 
ther. There is no trace of comminuted fossils in this space, as there 
is in most specimens that I have cut up. The whole of the re- 
mainder of the cavity is filled with a grecnish-grey spar, with a 
patch in the back part of the head at 6 of a different colour. This 
spar holds avast number of small ovate bodies (fig. 4), of which the 
greater diameter is about an eightieth of an inch, and the: lesser a 
hundredth. They are of a lighter colour and more opaque than the 
matrix. When examined with a good glass, and under favourable 
light, they seem to float, as it were,in the spar. The hypostoma 
c d, is in place, and is here cut through. From the end of the tail, 
at ¢c, a thin rough line runs inwards, nearly to the large spot at f, 
and is obscurely indicated thence to the end of the hypostoma 
atc. The spot f appears to be organic. It is of an ovate form, 
and has four or five obscure ribs across it at right angles to its 
greater diameter. There are other dark spots scattered irregularly 
throughout the matrix, that possibly*may represent organic struc- 
tures. 
It is possible that the line e fc may represent the edge of the 
ventral integument cut through; for in a rolled-up trilobite this 
must be exactly its position. The small ovate bodies I believe to 
be the eggs, 
