- a 
/ 
, 
p' : 
MarcH 7, 1884. ] 
and Ceéraurus, there was always some doubt 
about the number of appendages that were to 
be assigned to the pygidium. That they were 
jointed and not foliaceous appendages, I had 
no doubt, and so stated it in the text,’ and 
also in the restoration, of which fig. 2 is a 
copy. 
Fie. 2.— Under side of Calymene senaria as figured in Bull. 
mus. comp. zool., vol. viii. pl. vi., 1881. H,hypostoma; J/, 
mouth; A, abdominal appendages. 
The leg beneath the thorax of the Ohio 
trilobite shows seven joints in two instances: 
the character of the terminal joint is un- 
known. . 
The discovery of this unique specimen fully 
establishes the correctness of the restoration 
made by the writer of the ambulatory appen- 
dages of Calymene, as shown in fig. 2. The 
few traces of the branchial filaments do not 
differ from those described as occurring in the 
genera Calymene, Ceraurus, and Acidaspis. 
From the evidence given, there appears to 
be no necessity for a change in the classifica- 
tion of the trilobites given on pp. 209, 210 
(ibid.) : — 
Class, Poecilopoda; sub-class, Palaeadae ; 
order, Trilobita. 
Trilobita: ex., Asaphus, Calymene, etc. 
1. Eyes sessile, compound. 2. Ocelli un- 
known. 3. Cephalic limbs serving as mouth- 
1 Bull. mus. comp. 206l., vol, viii. p. 204, 1861. 
SCIENCE. 
281 
organs. 4. Thoracic segments bearing jointed 
legs and attached branchiae. 5. All segments 
bearing appendages. 6. Thoracic segments 
unanchylosed. 7. Abdominal segments an- 
chylosed, and bearing jointed appendages. 8. 
Hypostoma large (metastoma unknown). ‘To 
section 7 we now add ‘ (similar to those of 
the thorax).’ 
The attempt to locate the branchial appara- 
tus of the trilobite beneath the pygidium is not 
surprising when a comparison with Limulus 
and Serolis is made with those trilobites hay- 
ing a large pygidium; but in such genera as 
Conocephalites, Arionellus, and others having 
a pygidium very small, as compared with the re- 
maining parts of the animal, the necessity for a 
different branchial system is at once apparent. 
The director of the Geological survey of 
Canada having given permission to have the 
original specimen of Asaphus platycephalus, 
described by Mr. Billings as showing ambula- 
tory. legs, sent to me, Prof. J. F. Whiteaves 
kindly forwarded it; and the specimen was 
placed by the side of the Ohio trilobite for 
comparison. A glance showed that Mr. Bil- 
lings’s interpretation was the correct one, and 
that, as far as the thoracic legs are considered, 
the Canadian trilobite has a pair for each seg- 
ment. Of the abdominal legs nothing is seen. 
The only addition to our knowledge of the 
structure of the trilobite, furnished by the Ohio 
specimen, is the verification of the hypothesis 
that the legs were jointed beneath the pygidium, 
as shown in the sections of Ceraurus and 
Calymene, and expressed in fig. 2. 
Fie. 3. — Cross-section of fig. 2. s, dorsal shell; 7, alimentary 
canal; B, spiral branchiae; e, epipodite; Z,leg. Taken from 
same plate as fig. 2. In some instances the branchial fila- 
ments or ribbons are straight and not spirally coiled. 
That the trilobites and crustaceans were 
differentiated before the existence of the oldest 
Cambrian fauna we now know, is my present 
belief, the two classes coming down on two 
distinct lines of descent. In a paper now in 
the course of preparation, the entire subject 
will be reviewed, and illustrations given of the 
different orders of the class Poecilopoda. 
Cuartes D. WaAtLcort. 
