FRESH-WATER FISHES OF SIAM, OR THAILAND 233 



In the Thai vernacular this fish bears a variety of names in different 

 localities. The most common are fla hua Hem (angular-head fish) 

 and pla hang huang, heard in the basin of the Menam Chao Phya. At 

 Chiengrai the fish is called pla Mom hang wong. 



Genus TYLOGNATHUS Heckel 



Tylognatlius Heckel, in Rueseggei's Reisen, vol. 1, pt. 2, p. 1027, 1843. (Type, 

 VaricorMnus diplostomus Heckel.) 



I The genus Tylognathus, as proposed by Heckel (1843), was com- 

 posite. Bleeker (1863 [314]) made VaricorMnus diplostomus Heckel 

 from Kashmir the type of the genus, a species placed by Giinther and 

 Day in the genus Labeo. If this disposition of diplostonvus is sound, 

 Tylognathus is not a tenable name for these or other fishes, and both 

 Tylognathus and VaricorMnus may be synonyms of Labeo. 



The availability of the name Tylognathus was questioned by Jordan 

 (1919, pt. 2, p. 211). Hamilton (1822) set aside a group of 10 cypri- 

 noid fishes having, among other features, a median postsymphyseal 

 longitudinal ridge on the inside of the lower jaw as in the sea mullets, 

 and called them Bangana, this being a vernacular Indian name for 

 fishes of the genus Mugil. Jordan made Hamilton's dero the type 

 of Bangana^ it being the first species mentioned, and stated that Ban- 

 gana "probably replaces Tylognathus Heckel and Lohocheilus van 

 Hasselt." Specimens of dcro supplied by the Indian Museum in Cal- 

 cutta, through the courtesy of Dr. S. L. Hora, do not have a post- 

 symphyseal ridge as called for by Hamilton's definition of the genus, 

 and this species is identified by Hora and others as a Ldbeo. Tylog- 

 nathus of Heckel and Lohocheilus of van Hasselt lack this feature. 

 It is believed that Jordan was in error in this view. 



The figure of a Tylognathus given by Weber and de Beaufort (1916, 

 vol. 3, p. 219, fig. 88) and their definition as affecting the lower lip 

 pertain to Lohocheilms^ as herein conceived. Dr. de Beaufort, in des- 

 cribing a new species of Tylognathus from Thailand ( T. siam^ensis) , 

 drew attention to the differences between it and Indo-Australian 

 forms : 



The structure of the lower lip in this species differs somewhat from that 

 in Indo-Australian species, the only ones I am acquainted with. In the last- 

 named we can recognize (see Weber & de Beaufort, Fishes of the Indo-Australian 

 Archipelago, Vol. Ill, p. 219) a median part of the lower lip, which is much 

 enlarged and swollen, and expanded laterally so as to cover the lateral parts of 

 this lip, which are continuous with the upper lip round the corner of the 

 mouth. To see those lateral parts one has to lift the median part. In the 

 species described above this median part is much smaller and does not cover 

 the lateral parte. Another difference is noticeable in the lower jaw. This Is 

 covered in Indo-Australian species by a very thick mass, probably consisting of 

 connective tissue and forming a sharp transverse ridge in front. This ridge 

 is present also in the Siamese species, but the thick pad is not developed here. 



