Dr. A. Giinther on new Freshwater Fishes. 475 



0. pallida^ Marrat, will not agree with any figure or de- 

 scription of 0. scripta^ Lam. There is a very considerable 

 difference between the 0. scripta, Lam., as figured by Reeve, 

 and the 0. scripta^ Lam., as figured by Duclos ; and a much 

 greater difi'erence exists between the shells in my cabinet and 

 the forms figured. 



0. similis^ Marrat, is so decidedly distinct as to require no 

 comment. 



2 Peveril Terrace, Edge Laue, Liverpool. 

 May 16, 1808. 



LVI. — Diagnoses of some new Freshwater Fishes from. Suri- 

 nam and Brazil, in the Collection of the British Museum. 

 By Dr. Albeet Gunther. 



The Trustees of the British Museum obtained, in the course 

 of last year, several collecti.>ns of South-American Fishes, 

 of which we may mention that made by Mr. Edward Bartlett 

 on the Huallaga and at Xeberos (Upper Amazons), others 

 sent by Hr. Kappler from the Maroni River (Surinam), 

 and, finally, numerous examples from Surinam, formerly in 

 the museum of the late Dr. van Lidth de Jeude. For the 

 present I give the diagnoses of those species which I have 

 found to be undescribed ; and more detailed descriptions with 

 illustrations will be published in the ' Proceedings of the Zoo- 

 logical Society,' before which the paper was read on March 26. 



Doras helicophilus. 



Lateral shields well developed, entirely uncovered by the 

 skin ; the depth of the third is one-half of the length of the head, 

 those on the tail only half as deep as the tail ; their whole 

 surface is covered with minute spines. Humeral process 

 without spines, with a very slight ridge extending to the 

 hinder third of the pectoral spine. The posterior lobes of the 

 nuchal carapace are rounded, reaching to the base of the se- 

 cond soft ray of the dorsal fin. Dorsal spine serrated in front 

 and behind, the anterior denticulations being directed upwards. 

 Caudal peduncle shielded above and below. Uniform blackish ; 

 dorsal fin white, the middle black. 



Surinam. 



Oxydoras acipenserinus. 



This fish is distinguished from all its congeners by the pe- 

 culiar shape of the head and snout, which is elongate triangular, 

 pointed, and much depressed in its anterior portion. L. lat.42. 



Xeberos. 



33* 



