Pineal Eye in Extinct Vertebrates. 915 
measures of Pennsylvania (Plate XV), which is intermediate in the 
character of the anterior regions between Cephalaspis and Bothri- 
olepis. The median orifice of the latter genus is present, and its 
middle portion is roofed by a plate. But this plate differs from 
that of Bothriolepis and Pterichthys, in being perforated by two 
orifices, which resemble in their position nostrils, while the lateral 
orifices have the position of the eyes of the Cephalaspidide. 
Under these circumstances the evidence in favor of the orifices in 
Bothriolepis being eyes, is stronger than that which points to its 
homology with the mouth of Tunicata. The structure of these 
primitive vertebrates strongly indicates the origin of lateral or 
paired eyes from a single median eye, such as is found in the Tunicata, 
and continues to point to the descent of Bothriolepis from those ani- 
mals. Mycterops indicates a wider divergence than Bothriolepis ; and 
Cephalaspis a still further stage of modification. Dr. Dollo, of 
Brussels, has expressed the view that the superior orifice of Pter- 
ichthys corresponds with the median eye of the Tunicata and the 
pineal eye of the Reptilia. 
Of course, if the median eye of the Tunicata became specialized 
into the lateral eyes of higher vertebrates, it might seem improbable 
that it could be at the same time homologous, as there are no em- 
bryological reasons for refusing to believe (Spencer), with the pineal 
eye of the same forms, which possess also the lateral eyes. It may 
not be impossible, however, that this is really the case, and that the 
paired eyes, as well as the pineal eye, have been formed by evagina- 
tion of differentiated parts of the Tunicate eye, so that the views of 
Lankester and Spencer may be both correct. The formation of the 
lens from two parts in the Tunicates, which precludes its corres- 
pondence with the pineal lens in Reptilia, probably has a significance 
in this connection, expressing the origin of the lateral eyes, while 
the retinal portion is homologous with the pineal retina. 
In extinct American Batrachia: bate ee foramen is wanting 
in Eryo; 1Za trachys, and | ved in Trimerorhachis; 
but it is well developeds i in Cricotus, the genus that leads probably 
to the Reptilia. 
Among North American extinct reptiles I have described the 
characters ' of the cast of the brain case in two widely distinct forms. 
1 Proceeds. Amer. Philos, Soc., 1886, p. 234. 
