Diagnosis: Notoglanidium thomasi differs from all congeners in the large interorbital distance, 41.0-46.7% of head length vs. less than 37% in all other species (Ref. 94168). It differs from other species in the genus in having: a rather large eye diameter, 9.1-12.5% of head length vs. smaller in N. depierrei, N. maculatum and N. pallidum; a small combined premaxillary tooth plate width, 11.9-18.2% of head length vs. larger in N. akiri, N. boutchangai, N. macrostoma and N. pembetadi; and a relatively large number of soft dorsal-fin rays, 12-16 vs. less in N. akiri, N. boutchangai, N. depierrei and N. macrostoma (Ref. 94168).

Description: Body slender but not elongate, about 7-9 times as long as deep, predorsal body depth 16.1-19.2% of standard length, minimal caudal peduncle depth 10.7-13.1% of standard length; head not depressed, head depth 52.2-65.2% of head length (Ref. 57126, 94168). Occipital process scarcely developed and well separated from nuchal plates; humeral spine well visible (Ref. 57126). Eyes very small, round and in dorsal position (Ref. 57126). Branchiostegal membranes completely fused (Ref. 94168). Dorsal fin with short spine, 4.6-6.2% of head length; adipose fin low, 1.2-4.5% of standard length (Ref. 94168).

Colouration: In life, light brown with many round to irregular, large spots covering most of the head and body surface, leaving little space in between; spots are smaller ventrally and on the caudal fin; spots on pectoral, pelvic and anal fins very faint (Ref. 94168).