Dine BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Of the halibut, Hippoglossus hippoglossus, thirteen specimens were 
examined, twelve dextral and one sinistral, and in all the left optic 
nerve was dorsal, thus confirming the statement of Owen (’66, p. 300) 
for this species. Of the bastard halibut, Paralichthys californicus, 
twenty-six were examined, eleven sinistral and fifteen dextral, and in 
all the right nerve was dorsal. Of the starry flounder, Platichthys 
stellatus, one hundred were examined, fifty sinistral and fifty dextral, 
and in all the left nerve was dorsal. It therefore appears that each 
of these three species has a monomorphic chiasma irrespective of the 
fact that it may be composed in part of sinistral and in part of dextral 
individuals, and, therefore, the conclusion is that, at least in these 
species, the manner of the crossing of the optic nerves is independent of 
the type of migration shown by the eye. 
The three species mentioned seem at first sight to be exceptions to 
what has been said of the Pleuronectidae in general, but such is not 
wholly true. Each species, as in the other Pleuronectidae examined, 
has a monomorphic chiasma, and the nerve that is dorsal in each instance 
is the one that would reasonably be expected to be. ‘Thus, in the halibut 
the species is essentially dextral, for sinistral individuals are extremely 
rare,’ and in conformity with this the left nerve is always dorsal. The 
bastard flounder belongs to a genus all other American members of which 
are sinistral; it is therefore natural to find that in this species, though 
it contains both dextral and sinistral individuals, the rule for a sinistral 
form holds, the right nerve being always dorsal. The starry flounder 
is a member of the Pleuronectinae, a subfamily in which this species is 
almost the only American exception to complete dextrality, and as 
usual the rule for dextral species prevails, all left nerves being dorsal. 
These species, therefore, conform perfectly to the rule for other Pleu- 
ronectidae that prescribes a monomorphic chiasma, and though in them 
the dorsal nerve is not always connected with the migrating eye, it is 
always connected with that eye which in the greater number or nearest 
of kin is the one to migrate. Thus these species are not so exceptional 
as they at first appear. 
Of the two conditions presented by each of the three species men- 
tioned one may be said to be typical and the other atypical. The 
typical condition is represented by the dextral halibuts and starry floun- 
ders and by the sinistral bastard halibuts ; the atypical condition by the 
1 The sinistral halibut examined by me was the only individual obtained dur- 
ing the winter of 1900-01 by one of the largest halibut establishments in Boston. 
It was certainly a single individual in many thousands. 
