The psammophilic trichomycterid genus Typhlobelus is rediagnosed on the basis of additional synapomorphic characters, including: 1) the premaxilla displaced posteriorly, and connected to shaft of the mesethmoid rather than to its anterior tip; 2) the premaxilla with complex tridimensional shape, with a large dorsal process directed mesially and bearing teeth (when present) on the lateral end only; 3) the dentary portion of the coronoid process expanded into a broad plate; 4) the palatine club-shaped and oriented obliquely relative to the longitudinal axis of the skull; 5) the semi-discoidal anterior portion of the mesethmoid; 6) the laminar anterior ascending process of the quadrate lacking a cartilaginous tip; 7) hyomandibula with a long posterior process; 8) the neural arch of the Weberian complex ring-like and forming two large dorsal foramina at its border with the supraoccipital; and 9) the basibranchials and hypobranchials poorly differentiated or absent. Additional diagnostic characters are presented for the species currently included in Typhlobelus. A new species of the genus, Typhlobelus auriculatus, from the Rio Xingu in northern Brazil, is uniquely diagnosed from all other trichomycterids, and probably from all other catfishes, by the presence of a well-defined lateral pit immediately posterior to the head, representing a modified pseudotympanus connected by a superficial groove to a pit entering the skull. The species is also unique in the lack of any laterosensory pores on the body or head. The new species is further distinguished from its congeners by the absence of an anal fin and by the presence of opercular odontodes, in addition to other characters of internal and external anatomy.
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