1870.] BILLINGS—LOWER-SILURIAN TRILOBITES. 481 
A short notice of the specimen was drawn up and read before the 
Natural-History Society of Montrealin 1864. Publication, however, 
was delayed, partly because I hoped to obtain additional evidence, 
but principally because I wished to have the specimen first exhi- 
bited to the Geological Society, and examined by as many of the 
Fellows as possible. Fecling somewhat apprehensive that it would 
be difficult to persuade geologists and paleontologists into the belief 
of the existence of trilobitic legs by figures and descriptions alone, 
I thought it bette® to wait until the paper and the specimens could 
be laid before the Society at the same time. 
During the six years that have elapsed,'a vast number of Trilo- 
bites have passed through my hands, but nearly all of them in a 
fragmentary condition. Among such, I am’ satisfied, we may seck 
in vain for any traces of locomotive organs.) We can only cxpect 
to find them in perfect or nearly perfect specimens. These latter, 
considering the prodigious multitude of these animals that must 
have existed in the Silurian and Devonian seas, are not abundant 
fossils; at least they are not so in our Canadian rocks. For ex- 
ample, during the twenty years that I have collected fossils, I do 
not believe that I have scen fifty specimens of A. platycephalus with 
with the head, thorax, and pygidium all in connexion. We have 
had a number of those belonging to the provincial collection cut up 
and polished, without any success whatever. They were not the 
best ones, but they were as perfect as was the subject of this notice 
before it was split apart. There are others in the collection which 
may have the underside preserved; but we do not like to sacrifice _ 
them. Although no additional evidence of the existence of limbs 
was discovered, several points in the structure of other parts were 
ascertained, which will be described further on. As Sir W. KE. Lo- 
gan is about visiting London, and has kindly offered to take charge 
of this paper, and will also take the specimens with him, I shall 
delay publication no longer. 
2. Discovery of the Panderian Organ* in several American species 
of Asaphus. 
The evidence afforded by the specimen above described, and others 
of which I have made sections, proves that in the genus Asaphus 
the underside was not flat, but somewhat concave. In thehead, on 
each side of the mouth, there was a cavity like that which occurs in 
the existing king crab—JLimulus Polyphemus. The position of these 
cavities is at cc,in Pl. XXXI. fig. 1. They are partially filled up 
in the specimen; but I have ascertained their depth to be about five 
lines in another individual of the same size. The ends of the 
pleure projected downwards a short distance below the level of the 
sternum. ‘The pygidium was also concave at the sides, with a por- 
tion along the middle, holding the intestine, convex. This structure 
can be seen, in part, by examining the slab from which the specimen 
* Dr. Volborth calls the organs in question “die Pander'schen Organe,” a term 
of which I heartily approve, as, if generally adopted, it will permanently asso- 
ciate Dr. Pander’s name with his discovery. 
