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Fishery Bulletin 96(4), 1998 
and Pleuronectinae. Three synapomorphies defining 
this lineage (Fig. 6) are spines absent on gill rakers 
(13, Fig. 3, C and D); anterior margin of upper orbit 
complete with an overlap between mesethmoid and 
prefrontal of the blind side ( 14, Fig. 8, C and D); and 
first anal pterygiophore broadly thickened (15). 
Exceptions to the distribution in these synapo- 
morphies are found in Pleuronectinae and Hippo- 
glossinae. The anterior margin of the upper orbit is 
incomplete in Microstomus achne, M. bathybius, M. 
kitt, M. pacificus, Pleuronectes pinnifasciatus, 
Pseudopleuronectes americanus, P. herzensteini, and 
P. yokohamae. Reinhardtius stomias, which also has 
the derived state for this character, is excluded from 
this third lineage. The first anal pterygiophore is not 
thickened in Microstomus achne, M. bathybius, M. 
kitt , and M. pacificus , whereas in Hippoglossus and 
Verasper (Hippoglossinae) the first anal ptery- 
giophore is broadly thickened. 
The fourth lineage (IV) includes all species of 
Hippoglossoidinae and Pleuronectinae. The sister re- 
lationship between these two subfamilies is deter- 
mined by seven synapomorphies (Fig. 6): dentition 
of uniform size (16, Fig. 9, B-D); interorbital process 
reduced or completely absent (17, Fig. 10, B, D, and 
E); hyomandibula broadened anteriorly (18, Fig. 2D); 
dentition on third epibranchial absent (19, Fig. 3, C 
and D); bony plates absent on branchial arches (20, 
Fig. 3, C and D); two rows of teeth present on fourth 
ceratobranchial (21, Fig. 3, C and D); and dorso- 
posterior margin of operculum fimbriated (22, Fig. 
2, B-D). 
Exceptions to these character distributions are 
found in only two species of Hippoglossoides and in 
Microstomini. Hippoglossoides platessoides and H. 
robustus have larger anterior teeth (16) that were 
historically termed as “canines” (Norman, 1934). 
Glyptocephalus kitaharai, G. zachirus, Microstomus 
achne, M. kitt, M. pacificus, and all species in 
Pleuronichthys have an interorbital process (17, Fig. 
10C). The anterior margin of the hyomandibular (18) 
is not broadened in Glyptocephalus and Microstomus 
(Fig. 20. Dentition on the third epibranchial and 
bony plates on branchial arches are observed in 
Pleuronichthys guttulatus . The number of rows of 
teeth on the fourth ceratobranchial are reduced to 
only one in Glyptocephalus , Platichthys bicoloratus, 
and Pleuronichthys and are absent in Limanda 
punctatissima. Fimbriation of the operculum (22) is 
also observed in Flippoglossinae (Fig. 2B) but is ab- 
sent in the Eopsettinae and Lyopsettinae. This last 
exception suggests that fimbriation of the operculum 
may be synapomorphic for Pleuronectidae because 
only Eopsetta grigorjewi, E. jordani, and Lyopsetta 
