1856.] 177 



more protruding. The scales ai-e either large, or else of moderate size, and the 

 lateral line follows more or less the middle of the flanks. The dorsal fin is 

 higher than long, and shorter than in Iliihorynchus, and the anterior ray is more 

 closely united to the next. The insertion of the ventrals is always situated 

 posteriorly to the anterior margin of the dorsal, or under it, never in advance of 

 it. The caudal is treated. The pharyngeal bones are stouter than in Hyboryn- 

 chus, the lower branch or limb has the same length as tlie upper ; both are 

 more curved, thus rendering the convexity of that bone more conspicuous ; it is 

 expanded as usual. The teeth are similar to those of Hyborynchus^ being, how- 

 ever, not quite so compressed and not hooked. Four are observed upon one 

 single row : 4 4. 



This genus is closely allied to Campostoma, and since our DiondfB are, gene- 

 rally speaking, small fishes, we should not be surprised at hearing that some of 

 the species of Campostoma, while yet immature could not always be easily dis- 

 tinguished from them, for the mouth is, properly speaking, not smaller than in 

 Cainpostoma. 



The following species have fallen under our observations. 



] . DioNDA EPiscopA. Slcudcr and graceful, fusiform in profile and compressed, 

 with the back slightly arched. The head is large, forming about the fifth of 

 the length. The eye is large and subcircular, its diameter being contained three 

 times and a half in the length of the side of the head. The fins are of but mode- 

 rate development ; the insertion of the ventrals is situated a little posterior to 

 the anterior margin of the dorsal. The rays read as follows : 



D 8+2 ; A 8+2 ; C 8, 1, 9, 8, 1, 7 ; V 8 ; P 14. 



The scales are large, the lateral line following the middle of the flanks. 



The dorsal region is blackish brown ; a black vitta is observed along the flanks, 

 just above the lateral line, extending from a black spot, upon the base of the 

 caudal, to the extremity of the snout. The inferior region is yellowish white 

 spread over with minute black dots. 



Collected in the head waters of the Rio Pecos, and brought home by Capt. 

 John Pope, U. S. A. Specimens of the same species were caught by John H. 

 Clark, under Col. J. D. Graham, U. S. A., in Camanche Spring, a presumed 

 tributary of the Rio Grande del Norte (Rio Bravo), or more probably without 

 outlet. 



2. DiONDA SERENA. Could easily be mistaken for D. episcopa. Its form is 

 slender and elongated, the dorsal outline being nearly straight 5 the head enters 

 five times and a half in the total length. The eye is large and circular, its di- 

 ameter entering only three times in the length of the side of the head. The in- 

 sertion of the ventrals takes place immediately opposite the anterior margin of 

 the dorsal fin. The pectorals are long and slender, more so even than in D. 

 episcopa. 



The dorsal region is light brown, the flanks and abdomen being silvery, with 

 the scales of the lateral line dotted with black, imitating spots. A black spot 

 upon the base of the caudal fin. 



From the Rio Sabinal, Texas ; collected by Dr. 0. B. Kennerly, under W. H. 

 Emory, Commissioner U. S. and Mex. Boundary. 



3. DioNDA TEXENSis, is a vcry characteristic species. The body is rather 

 deep upon its middle, and the lateral line somewhat depressed. The head is 

 quite small and subconical, entering five times and a half in the total length. 

 The eye is large and circular. The insertion of the ventral fin is placed a little 

 posteriorly to the anterior margin of the dorsal. The dorsal region is gre3'ish 

 brown ; the abominal region greyish white ; a diffused greyish black band may 

 be observed along the middle of the flanks, embracing the lateral line beneath, 

 and a black spot upon the base of the caudal. The ventrals and pectorals are 

 yellow. 



Numerous specimens were collected in the Rio Nueces, Texas, by John H. 

 Clark, under Col. J. D. Graham, U. S. A. 



14 



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