Species delimitations in the Atractus collaris complex (Serpentes: Dipsadidae) Author Passos, Paulo Author Prudente, Ana L. C. Author Ramos, Luciana O. Author Caicedo-Portilla, José Rances Author Lynch, John D. text Zootaxa 2018 2018-03-12 4392 3 491 520 journal article 30550 10.11646/zootaxa.4392.3.4 6b2ac420-3c8e-429e-9497-562945198c5a 1175-5326 1196169 8621C6F2-C541-4771-A813-3034CC3E352D Key to the known species of the Atractus collaris species group In order to simplify field and laboratory identification, this key is mainly based on external morphology but we must employ a few traits also from internal morphology (e.g., maxillary dentition) or sexually dimorphic characters (e.g., hemipenial morphology). However, whenever we use more restricted (or of difficult observation) characters they are in combination with other externally discernible characteristics. In general, the use of more than one character in all of key steps improves the reliability of the identifications. Finally, we highlighted that this key was conceived on the basis of available sample, which may underestimate taxa polymorphism and, therefore, we recommend to it be complementary to species diagnoses. 1. Loreal scale generally in contact with the first surpalabial scale, usually six maxillary teeth........................... 5 - Loreal scale isolated from the first supralabial by postnasal scale, usually four or five maxillary teeth................... 2 2. Hemipenis bilobed, dorsum lacking conspicuous paravertebral spots in preservative, and CL/SVL ± 9.2 in females and <14.0 in males............................................................................................. 3 - Hemipenis unilobed, dorsum with paravertebral spots in preservative, and CL/SVL Ż 9.2 in females and 14.0 in males..... 4 3. Ventral scales> 199 in females, internasal separated from loreal scale by postnasal scale, dorsum uniformly black in preserva- tive, and CL/SVL < 9 in females................................................................. A. surucucu . - Ventral scales < 190 in females, internasal usually in contact with loreal scale, dorsum with barely defined paravertebral spots and occasionally vertebral line in preservative, and CL/SVL Ż 9.0...................................... A. caxiuana . 4. Hemipenis with sulcus spermaticus divided distally, ventral scales> 173 in males and> 195 in females.......... A. zidoki . - Hemipenis with sulcus spermaticus undivided, ventral scales < 172 in males and < 181 in females.......... A. hoogmoedi . 5. Ventral scales Ż 200 in females and> 184 in males, and subcaudal scales> 35 in males and Ż 24 in females, single postocular in females, presence of vertebral line, and females with a single postocular scale at least on the one side of the head............................................................................................ A. gaigeae . - Ventral scales < 200 in females and < 184 in males, and subcaudal scales < 35 in males and ± 24 in females, two postocular in both sexes, usually lacking vertebral line, and females with tow postocular scales.................................. 6. 6. Hemipenis with calcified alary spines, hemipenial lobes and sulcus spermaticus centrifugally oriented, and dorsum uniformly dark brown or black usually lacking spots in preservative........................................ A. alphonsehogei . - Hemipenis with alary spines lacking calcification, lobes and sulcus spermaticus centrolinearly oriented, and dorsum with conspicuous white bordered spots in preservative....................................................... A. collaris .