EDWIN CHAPIN STARKS 7 



species (The Freshwater Fishes of British Guiana). Material at hand from 

 Para represents two distinct forms, which seem to be referable to this and 

 the following species. 



Seven specimens were collected in the market at Para, and one near the 

 mouth of the Madeira River (by Mr. Mann and Dr. Baker). They are 

 from 10 to 20 inches in length, or measuring the length of the disk only, 

 from 5 to 11 inches. In these the preoral part of the snout is contained 

 in the length to the front of the vent from 4 to 4^ times. The width of 

 the mandibular tooth-patch is contained from 13 to 13^ times in the same 

 length. The interspiracular width is contained from 1^ to 1^ times in 

 the length of the snout from the eyes. The teeth are stained brown in all 

 of the large specimens, and usually in the small ones. Counting the longest 

 rows of teeth in the mandible from the outer side obliquely to the median 

 line they number from 12 to 14. The largest papillse behind the teeth are 

 about 3 times longer than broad, and nearly or quite half as long as the eye. 



The color is variable. All of them are light dusky brown with lighter 

 spots scattered over the back of cream or light sienna color. The spots are 

 with blended edges shading into the ground color. Surrounding the spots 

 at some distance from their edges are usually elongate, irregular, black 

 blotches forming more or less regular broken rings of greater diameter than 

 the eye. In one or two of the smaller specimens the rings are nearly com- 

 plete, but in one they are entirely absent. Usually the black spots forming 

 them are sharp-edged and very definite, but occasionally they are soft and 

 blended. Sometimes they are so separated that they scarcely suggest rings, 

 but run irregularly in various directions. The side of the tail is very dis- 

 tinctly barred with alternate light and dark spots. 



10. Potamotrygon motoro (Miiller and Henle). 



Three specimens from 11 to 22 inches in length (or measuring the disk 

 only, from 6 to 12 inches) were collected in the market at Para. 



The preoral part of the snout is longer than in P. hystrix, being con- 

 tained in the length to the front of the vent from 3^ to ZYz times. The 

 width of the mandibular tooth-patch is contaiiled 10^^ to 11 times in the 

 same length. The interspiracular width is contained 1^ times in the snout 

 from the eyes. The teeth are not stained brown and the longest rows from 

 the outer side to the middle of the mandibular patch number 19 or 20. The 

 longest papillae in the mouth are scarcely longer than broad, and do not 

 exceed the length of the pupil. The disk is more thickly set with fine 

 spinules than in P. hystrix, so that it is more like ordinary shagreen. 



