


SCHISMATORHYNCHOS REVISION 
99 

Fig. 1 Outline drawings of oro-labial structure of: A. S. heterorhynchos, MZB unregistered, mm SI; B. S. holorhynchos, USNM 325389, 101.7 mm SI; C. 
S. endecarhapis, MZB 6092, 179.0 mm SI; D. Lobocheilos bo, BMNH 1993.5.19:1, 87.0 mm SI; E. Tylognathus diplostomus, BMNH 1932.2.20:7, 215.0 
mm SI. ELJ=edge of lower jaw; F=frenulum; LL=lower lip; M=mouth; MLL=median lobe lower lip; PG=postlabial grove; RC=rostral cap; UL=upper 
lip. 
rhynchos develop from structure general for labeonin cyprinids, 
exemplified by Tylognathus diplostoma (Heckel, 1838)(Fig. 1E ) 
and similar to that of Tylognatus nukta (Hora, 1942: Fig. 9b; see 
Reid, 1985:p. 287 for the assignment of Labeo nukta to Tylognathus). 
At < 30 mm S| oro-labial structure of individuals of Schismato- 
rhynchos is like that of T: diplostoma or T. nukta. At about 30 mm SL 
the cutting edge of the lower jaw elongates, eventually interrupting 
the connection between the upper and lower lips around the corner 
of the mouth. At about the same time the fold in the skin which 
separates the region of the mandibular laterosensory canal from the 
rest lower labial tissue deepens, eventually forming the structure 
Weber & de Beaufort (1916) referred to as the frenulum. Rather than 
connecting the lower lip to the gular region, this frenulum houses the 
mandibular laterosensory canal. As the cutting edge of the lower jaw 
elongates, the portion of the lower lip between the lateral edge of the 
lower lip and the principle lobe of the lower lip regresses, completely 
in the two new species, nearly so in S. heterorhynchos. 
Elongation of the cutting edge of the lower jaw progresses farther 
in S. holorhynchos and S. heterorhynchos and their mouths are more 
crescentic than that of S. endecarhapis; they are probably each 
other’s closest relative. 
Nukta Hora 1s considered by some recent authors to be a synonym 
of Schismatorhynchos (Jayaram, 1981; Eschmeyer & Bailey, 1990; 
Talwar & Jhingran, 1991). We do not agree with this assessment. 
Instead we follow Reid (1985), insofar as his exclusion of Nukta from 
Schismatorhynchos, and our diagnosis excludesNukta fro mSchismato- 
rhynchos. Our reasons for supporting Reid are elaborated below. 
Hora (1942) erected Nukta as a subgenus of Schismatorhynchos 
for T. nukta (Sykes, 1841) in order to call attention to ‘the great 
similarity in the form of [S. heterorhynchos and T. nukta]’, by which 
he meant that both possess a deeply incised, heavily tuberculate 
snout, the upper lobe of which forms a projection from between the 
eyes. However, the outcome of the comparison between S. 
heterorhynchos and T. nukta was not straitforward. 
Whilst wishing to stress the similarity in the form of the snout 
between the two species, Hora also recognised that they differ so 
greatly in oro-labial structure that he also wrote ‘differences .. . in 
the structure of the lips and associated structures are of sufficient 
value to separate the two species generically’. Hora resolved the 
dilemma between the similarity in the form of the snout and the 
difference in oro-labial structure by subordinating Nukta under 
Schismatorhynchos. 
