FRESH-WATER FISHES OF SIAM, OR THAILAND 429 



16. Dorsal fin with fewer rays than in anal fin, and its origin behind that of anal ; 

 anal fin in male with the first ray elongated and modified, and several fol- 

 lowing rays elongated; species viviparous; maximum size about 7 cm. 



Derinogenys 



Genus HYPORHAMPHUS Gill 



Eyporhamphus Gnx, Proc. Acad. Nat. Sci. Philadelphia, 1859', p. 131, 1860. (Type, 

 HyporMmphus tricuspidatus Gill.) 



HYPORHAMPHUS UNIFASCIATUS (Ranzani) 



Hemiramphiis unifasciatus Ranzani, 1842, p. 326 (Brazil). 

 Eemirhamphus unifasciatus Hoea, 1924a, p. 472 (Tale Sap, inner lake). 



This widely distributed and common fish of the Indian, Pacific, and 

 Atlantic Oceans is represented in collections from Thailand by speci- 

 mens from the inner lake of the Tale Sap, as well as from the Gulf of 

 Siam. The first fresh- water specimens, four young, taken by Dr. N. 

 Annandale January 12-16, 1916, were reported on by Hora (1924). 

 Further specimens were obtained in the same locality by the writer 

 on September 27, 1924, and July 4, 1929, the largest example, 14.8 cm. 

 long, being taken in July. The water in the inner lake is fresh, and 

 the dates given indicate that the species may be a permanent resident, 

 although there is an open passage to the sea. 



The name applied to this fish by the local fishermen is pla tak. 



Genus ZENARCHOPTERUS Gill 



Zenarchopterus Gnx, Proc. Acad. Nat. Sci. Philadelphia, 1863, p. 273, 1864. (Type, 

 Hemiramphus dispar Cuvier and Valenciennes.) 



The nomenclature of the species of this genus is much confused. The 

 best account of the taxonomic and nomenclatorial questions involved is 

 by Mohr (1926a), who gives for the 13 species recognized a valuable 

 table, including a sketch of the dorsal and anal fins in the male of each 

 species. 



All of the members of this genus are viviparous and have secondary 

 sexual characters in the dorsal and anal fins and also in the shape of 

 the anal papilla. 



Five species are recognized from Thailand, with the following dis- 

 tinguishing characters : 



la. Upper jaw 2 times or nearly 2 times as long as broad. 



2a. Projection of lower jaw beyond upper jaw 4 times length of latter ; dorsal 

 rays in male apparently unmodified ; seventh anal ray in male enlarged 

 and thickened but not produced beyond other rays clarus 



26. Projection of lower jaw beyond upper jaw 2 to 3 times length of latter; 

 second to fourth dorsal rays in male enlarged and elongated ; fifth and 

 sixth or sixth and seventh anal rays in male enlarged and thickened 

 but not extending beyond other rays ectuntio 



