On a neio Fi£c'diid Fish from the Amazon. 659 



Type. Adult female. Original number 2188. Collected 

 on June 3rd, 1911. 



This Thamnomys is undoubtedly related to the large 

 Ruwenzori species, T. venustus, froui whicli it is distin- 

 guished by its greater size and far larger molar teeth. 



LXXITI, — A neio PoeciUid Fish from the Amazon, with Notes J 

 on the Genera Petalosoma and Tomeurus. By C. Tate 

 Regan, M.A. 



(Publislied by permission of tlie Trustees of the British Museum.) 



In 1908 (Ann. & Mag. Nat. Hist. (8) ii. p. 458) I described 

 a Pceciliid fish from Costa Rica under the name Petalosoma 

 cultratum ; this differed from all other Poeciliids then known 

 in having the tail behind the anal fin compressed to a sharp 

 ventral edge formed of paired scales. In the following year 

 Eigenmann (Ann. Carnegie Mus. vi. p. 53) published the 

 description of Tomeurus gracilis from British Guiana, another 

 Poeciliid fish with this peculiarity. I have now received 

 from Herr A. Rachow, of Hamburg, examples of a new 

 species of Petalosoma from the Amazon at Obidos. 



Petalosoma and Tomeurus resemble Gambusia in mouth- 

 structure, dentition, &c., and in having the anal fin of the 

 male advanced and modified into an intromitteiit organ. In 

 Petalosoma the body is moderately deep (depth 3 to •! in the 

 length) ; the anal fin of the male is inserted below or a little 

 behind the end of the pectoral, is rather short (^ to ^ the 

 length of the fish), and has the elongate rays simple ; the 

 pelvic fins are well developed, inserted below the middle of 

 the pectoral, larger in the male than in the female. In 

 Tomeurus {jide Eigenmann) the body is long and slender 

 (depth 6^ in the length), the anal fin of the male is inserted 

 below the base of the pectoral, is very long (^ the length of 

 the fish), and has the first elongate ray armed with spini- 

 ferous appendages, whilst the pelvic fins in the male are 

 minute, below the gill-openings, and in the female absent. 



The new species may be designated 



Petalosoma amazonum, sp. n. 



Body moderately compressed, its depth 3f in the length ; 

 length of head 4^. Snout as long as eye, the diameter of 

 which is 3 in the length of head and less than the intororbital 



