140 PROCEEDIlSrCS OF THE NATIONAL IMUSEUM vol.84 



Kegan's descriptions and figures of N. lankesteri, which has only 

 one first dorsal ray (see Myers, 1928), I do not think it can be that 

 species. I do not believe that it can be placed in any other genus of 

 Phallostethidae. This is the second species of phallostethid known 

 from Siam, and its discovery close to the Cambodian border makes it 

 appear certain that fishes of this family occur in Indo-China. 



Description. — First dorsal fin II. Second dorsal I, 5. Anal I, 

 151/2. Pectoral 12. Caudal with 12 branched rays and several 

 unbranched supporting rays above and below. Scales mostly lost, 

 but 31 pockets can be counted from head to caudal base. Nape and 

 head scaleless. Transverse scales between mid-dorsal series and 

 abdominal keel, at deepest part of body, Y. First dorsal origin over 

 base of eleventh branched anal ray. Origin of second dorsal over 

 base of last anal ray. Pectorals long and pointed, the upper rays 

 longest, reaching two-thirds of the distance from the upper part 

 of the fin base to the origin of the anal fin. Caudal forked. 



Measurements in millimeters (taken from point to point, as indi- 

 cated, with dividers, and not as to the vertical on the axis of the 

 fish) : Standard length 28.7. Depth (less abdominal keel) 6.3. Head 

 5.5. Snout tip to origin of second dorsal fin 23.0. Snout tip to origin 

 of anal fin 16.5. 



Anus and postanal papilla very similar to tliose of N. lankesteri 

 (see Regan, 1916, p. 16, fig. 12b). The papilla is less strongly bifid 

 than in that species, but, like it, one of the halves (left) is better de- 

 veloped. This may have some bearing on the occurrence of "rights" 

 and "lefts" among the males. 



Color (specimen fixed in formalin) pale j^ellowish, probably trans- 

 lucent in life. A black hair-line marking the division between the 

 epaxial and hypaxial trunk muscles from head to caudal. Another 

 fine black line along base of anal fin and middle of lower surface of 

 caudal peduncle to caudal fin. Above this line, on the anal base, is 

 another fine black line marking the junction of the body muscles and 

 the supports of the fin. A few black chromatophores along the 

 dorsum, a large patch on the occiput, another patch on the upper 

 surface of the snout, and one on the lower part of the pectoral girdle. 

 Other melanophores are dusted along the sides of the snout and jaws, 

 in a segment of a circle behind the eye, and on either side of the anus 

 and postanal papilla. Fins hyaline. 



Remarks. — There is a distinct possibility that this fish is identical 

 with N. lankesteri^ although only one first dorsal ray is reported for 

 that species. If Regan's figure (Regan, 1916, pi. 1, fig. b) of N. 

 lankesteri is correct in its proportions, which I see no reason to doubt, 

 N. siamensis differs otherwise in the greater depth and the much 

 more posterior positions of the dorsal and anal fins. 



