NATURAL SCIENCES OF PHILADELPHIA. 173 



greater than the thickness. The head forms scarcely less than a fourth of the 

 same. The snout equals the distance of the margin of the fifth scale of the 

 lateral line from the front of the eye. The breadth of the head at the occiput 

 equals half the length of the snout; at the eyes, little more than a third and 

 behind the nostrils, it enters 5J times in the same. The diameter of the eye 

 equals a sixth of the snout's length. The operculum is nearly as high as long, 

 subangulated behind, convex below at the anterior third, and thence advanc- 

 ing upwards towards the posterior margin. The ventral fins are nearer the 

 snout than the margin of the caudal, the latter extending about a third of 

 its own length beyond. 



D. (III.) 7. A. (III.) 8. C. (IX 2 ) 6+6. (IX 2 ) P. (I.) 13. V. (III.) 6. 

 8 



Scales 52-j-(at ventral between median dorsal and abdominal rows.) 



12 



The scales are nearly smooth ; in front deeper than long and obliquely con- 

 vex below; behind oblong rhombic and with rectilinear margins. Forty-five 

 scales precede the dorsal fin; the ventrals are behind the sixteenth oblique 

 row ; the anal behind the thirty-fifth and ending with the forty-first. Seven 

 rows of scales intervene between the lateral line and ventral fins. 



The color is glaucous above the lateral line and yellowish beneath. A spot 

 in front of the caudal above the lateral line ; others are on the forty-fifth and 

 forty-seventh rows of scales below the lateral line, and obscure ones on the 

 base of the caudal. 



This species is, for American Zoologists and Palaeontologists, the most inter- 

 esting fish of Oapt. Dow's fine collection. It is by far the most southern conti- 

 nental representative of the family that has been yet made known, the " Lepisos- 

 tens robolo 1 ' of Lacepede, founded on the Esox chilensis of Molina, not belonging to 

 this family. The only other species hitherto discovered beyond the boundaries 

 of the United States or Northern Mexico is a Cuban species of the same genu3, 

 the Atractosteus tri3toechus,Esoz tristocchus of Schneider and Lepidosteus manjuari 

 of Poey. The present species is distinguished by the form of the operculum, its 

 proportions and the large size of the scales. A single specimen, nearly sixteen 

 inches long, was obtained by Capt. Dow. 



Family TRYGONOIDJE. 



Genus UROTRYGON Gill. 



Urotrygon mundus Gill. 



The disk is orbicular with a slight linguiform projection in front and with 

 the pectoral fins behind broadly rounded. The distance of the snout from the 

 hinder margin of the pectorals equals the width of the disk. The tail (behind 

 the anus) is rather longer than the body (in front). The spine is inserted be- 

 hind the middle of the tail, and is about as long as the distance between the 

 snout and the nostrils. The ventral fins extend outwards, the rectilinear an- 

 terior margin tending little backwards, and the external margins are on a line 

 with and complete the outline of the disk. The posterior margin in the male 

 is nearly rectilinear, while in the female it is slightly convex, especially to- 

 wards the inner angles. The upper velum is very sinuous and fimbriated. The 

 teeth are pointed and pyramidal. The spiracles are oval, interrupted at the 

 intero-anterior angle by the eyes, and the margins are entire and well defined. 

 The skin is beset with numerous small stelliform tubercles, larger on the 

 dorsal region. The color is a uniform dark-brown above. 



Two small specimens, male and female, are in the collection. 



The present species would, by many zoologists, be referred to the genus 

 Urolophus of Miiller and Henle, but it would appear that it and the U. torpedinus 



1863.] 



