eo A 
414 The American Naturalist. [May, 
Metamerism in the Skull of Primordial Palzozoic Fishes. 
—One of the most interesting of recent discoveries is that by Dr. J. V. 
Rohon' regarding the fossils fishes of the genera Thyestes and Trematas- 
pis from the upper Silurian strata of the island of Oesel. Both genera 
belong to the order Aspidocephali. In Thyestes the cartilaginous 
primordial cranium falls into two distinct regions, anterior and poste 
rior, the former of which is bilaterally segmented, the latter not. On 
each side of the anterior region five segments are recognizable, the prox 
imal being joined to the middle skull mass, the distal portions being 
discrete, more or less pointed and arched behind. In the region of the 
second and third segments is the median frontal organ, between the third 
and fourth is the well marked optic capsule, while the parietal organ is 
‘above the fifth segment and between it and the hinder region of the 
skull. The hinder portion, representing the occipital region, is in form 
much like the body portion of the skeleton. Ventrally to it are appar- 
ently the remains of gill arches. Labyrinth and jaw apparatus are not 
differentiated. 
From these facts Rohon concludes that the Aspidocephali cannot 
belong to Cyclostomes, Selachians, Ganoids or Leptocardii. They must 
belong to a distinct subclass for which he proposes the name ; 
phali. The paper is a preliminary one and the complete article with 
plates will be awaited with interest. —K. : 
Mr. Rohon does not explain what he understands by the term Aspido- 
cephali. The genera Thyestes and Tremataspis have been hit 
included in the family Cephalaspide of the order Osteostraca of the sub- 
class Ostracophori of the class Agnatha. M. Rohon’s observations show 
that this systematic arrangement needs no modification, except pe 
the genera Thyestes and Tremataspis must be separated as & famiy 
distinct from the Cephalaspidæ.—C. 
The Auriferous Slates of the Sierra Nevada.—Ina recently 
published paper, Mr. J. P. Smith reviews the opinions of pe 
Writers as to the age of the auriferous slates of the Sierra hes 
after giving a brief statement of recent discoveries and determin? i 
of fossils from the beds in question, embodies the results of his! 
tions in the following conclusions : 
“The Auriferous slates are known to consist of Silurian, 
ous, Triassic and Jurassic strata.” Kim- 
7 The Mariposa slates are of Upper Jurassic, pr obably 10w =i 
meridge age.” 
Carbonifer- 
! Zool Anzsiger XVII, p. 51, 1894. 
