la. Gas bladder one-part with small fused terminal diverticula (Fig. 4A) _ 2
lb. Gas bladder two-part with fused terminal divertic ula expanded to form second bladder (Fig. 4B) 4
2a. Anterior midlateral plates moderate to deep (depth of 5th plate 24.4-34% of corresponding body depth) with subequal wings (depth of dorsal wing twice that of ventral wing or nearly so); postclei thral process short and broad (depth 36.8-53.6% of length); Amazonas/Essequibo basins _ 3
2b. Anterior midlateral plates shallow to moderate (depth of 5th plate 16.6-26.2% of corresponding body depth) with dorsal and ventral wings of equal depth (or nearly so); postcleithral process moder ately long and narrow (depth 23.9-34.5% of length); Orinoco basin _ Rhinodoras gallagheri, new species
3a. Sum of midlateral plates 61-64; postcleithral process extremely short and broad (depth 37.5 53.6% of length); adipose eyelid small to moderate (horizontal diameter 9.3-11.5% of head length); Amazonas basin (minus upper Branco) Rhinodoras boehlkei
3b. Sum of midlateral plates 57-60; postcleithral process moderately short and broad (depth 36.8 44.3% of length); adipose eyelid moderate to large (horizontal diameter 11.4-14.2% of head length); Essequibo/Branco basins_
Rhinodoras armbrusteri, new species 4a. Snout short (length 38.6-42.4% of head length); postcleithral process extremely long and narrow (depth 21.7-29% of length); tympanal plates moderately ossified, usually three evident, posteri or-most largest with strong medial thorn and moderately developed wings; pectoral fin usually 1,9 (range 1,8-10); Maracaibo basin Rhinodoras thomersoni
4b. Snout long (length 43.2-47.5% of head length); postcleithral process shorter and broader (depth 30.2-37.9% of length); tympanal plates weakly ossified, only one or two evident posteriorly as small plates or emergent thorns; pectoral fin usually 1,8 (range 1,7-9); Paraguay-Parana ba sin Rhinodoras dorbignyi

From:
Two New Species of Thicklip Thornycats, Genus Rhinodoras (Teleostei: Siluriformes: Doradidae)
Author(s): Mark H. Sabaj, Donald C. Taphorn and Otto E. Castillo G.
Source: Copeia, Vol. 2008, No. 1 (Mar. 21, 2008), pp. 209-226