Cnesterodon decemmaculatus (Jenyns, 1842) (Fig. 3) Poecilia decem-maculata Jenyns, 1842: 115, Plate 22. fig. 1, 1a. Type -locality: Maldonado [Uruguay]. BMNH 1917.7.14: 25, lectotype [by present designation]; BMNH 1917.7.14: 26, paralectotype. Maldonado. C. Darwin. Poecilia gracilis Valenciennes in Cuvier & Valenciennes, 1846: 133. Type -locality: environs de Montevidéo [Uruguay]. MNHN B-0939. Diagnosis. Cnesterodon decemmaculatus is diagnosed by the following autapomorphies: (1) bony style at gonopodium tip of large adult males relatively long, slightly arched, and covered by a wide membrane progressively narrowing towards tip forming a distal filament (Rosa & Costa, 1993; fig. 10); (2) membranous tip anterior to R4 and R5 absent [111-0]; and (3) membranous tip anterior to R4 and R5 absent [112-0]. Furthermore, C. decemmaculatus is readily distinguished from C. omorgmatos and C. raddai by dark brown blotches along body sides (forming bars vs. circular or irregular, respectively). Cnesterodon decemmaculatus is distinguished from C. carnegiei, C. hypselurus, and C. septentrionalis by dark bars on sides of body, mostly confined to midline, covering less than three scales in a transverse row, never extending to dorsal and ventral profiles (vs. dark bars of body very elongate reaching dorsal and ventral profiles, covering more than four scales in a transverse row). The absence of small scales covering lateral and ventral region of body below pectoral fin in adult females and the pointed snout distinguishes C. decemmaculatus from C. brevirostratus. Cnesterodon decemmaculatus is readily distinguished from C. iguape by the smaller post -gonopodium blotch on the ventral profile in adult males. Distribution. Lower rio Uruguay, laguna dos Patos system, Río Negro, Río Salado, western drainages of Argentina and small coastal drainages of Uruguay and Argentina (Fig. 1). Remarks. See Lucinda (2003) for discussion of type-locality.

Published as part of Lucinda, Paulo H. F., 2005, Systematics of the genus Cnesterodon Garman, 1895 (Cyprinodontiformes: Poeciliidae: Poeciliinae), pp. 259-270 in Neotropical Ichthyology 3 (2) on pages 262-263, DOI: 10.1590/s1679-62252005000200003, http://zenodo.org/record/5418097