1885. ] Geology and Faleontology. 291 
froy St. Hilaire, Owen and Lankester. On the other hand, in 
view of the absence of orbits, the theory of Ahlborn and Rabl 
Ruckard that these parts represent a primitive organ of sense or 
sight, must be taken into account. The close approximation of 
the orbits in some of the Cephalaspididze might add plausibility 
to this opinion. This would require us to believe that Pterich- 
thys is a monoculus, as it has no interorbital septum, and that the 
eyes of other Vertebrata have been derived from this single one 
by division and gradual separation of the halves. Such a view is 
not confirmed by the embryology of the eye, nor does it neces- 
sarily follow from the facts of palzontology. The resemblance 
between the median orifice of Pterichthys and the orbits of the 
Cephalaspidide is probably delusive, and the latter family has 
probably very remote affinity to the Pterichthyide. 
In view of the position of the mouth, it seems to me that this 
family should be removed from the Craniata to the Urochorda. 
It is true that the evidence that this orifice is a functional mouth 
is not entirely conclusive, as the transfer of the extremity of the 
cesophagus to the opening at the anterior extremity of the 
carapace may have taken place, as in the case of the anus. But 
there seems to be little doubt of the homology of the dorsal 
orifice with the mouth of Chelyosoma, and the structural resem- 
blance to it decides in favor of the Urochorda rather than the 
Marsipobranchii. Among Urochorda it differs from the Tuni- 
cata in the position of the anus, which is the normal vertebrate, 
and not the dorsal orifice of the former division. It will, there- 
fore, form a second order of the class Urochorda, which I pro- 
pose to call Antiarcha. : 
It may be more than a coincidence that while the Chelyo- 
soma is an arctic type, the Pterichthyidæ are so far only known 
from northern regions, Russia, Scotland, and the province of 
Quebec, Canada. ; i 
After an examination of at least fifty specimens of the Pterich- 
thys canadensis neither Mr. Whiteaves nor myself have been able 
concave as in the P. milleri, but is regularly rounded as in Chely- 
osoma. I suspect that the P. canadensis belongs to a genus dis- 
tinct from the P. milleri, which may, for the present, bear Eich- 
wald’s name Bothriolepis. The relations of Coccosteus to this 
order are not close, if the restorations given are correct, althou: 
it retains the same type of ventral plates —E. D. Cope. 
Types or CARBONIFEROUS XIPHOSURA NEWTO NORTH AMERICA. 
—We have received from R. D. Lacoe, Esq., of Pittston, Pa., for 
-study and identification, a valuable collection of Carboniferous 
Xiphosura, mostly from the Mazon Creek beds at Morris, Ill. 
Besides a series of Euproops dana, there is an undescribed spe- 
