NATURAL SCIENCES OP PHILADELPHIA. 269 



Total length, 1*7$ 100 



Greatest height 15 



Height behind last dorsal ray 5 



Thickness at pectorals 12 



Head Length 21 



Height over preoperculum 12 



Thickness at preoperculum 14 



" behind eyes 8 



Height at articulation of lower jaw 10 



Interorbital area 2 



Eye Diameter 2 



Distance from snout 3 



Dorsal Distance from snout (symphisis) 18 



Caudal Length 14 



Pectoral Length 22 



Ventral Length 12 



This species is very distinct from the two West Indian species of the genus. 

 It is readily distinguished by its different proportions. The head is longer, 

 wider and higher than in its congeners ; the caudal fin and especially the pec- 

 torals are larger, the number of dorsal and anal rays less, and the number of 

 scales through which the posterior or median part of the lateral line runs is 

 different. It is also readily recognizable by its different colors. The size to 

 which it attains is much less, the average length being little more than an inch 

 and a half. 



Three specimens were obtained by Mr. John Xantus, at Cape St. Lucas, and 

 have been sent by that indefatigable naturalist to the Museum of the Smith- 

 sonian Institution. 



Subfamily MYXODAGMN.<E Gill. 



The body is considerably elongated, the length being about ten times as 

 great as the height. 



The scales are moderate or rather small, cycloid, and with subcentral or 

 slightly eccentric nuclei and concentric striae. The lateral line at first is on 

 the side of the back, but is soon deflected and again runs in a straight line 

 along the middle of the sides towards the caudal fin ; then its end is again 

 deflected. 



The head is oblong or rather elongated, conical in profile, and more or less 

 transversely arched above. The skin is smooth. The operculum is fringed 

 behind. The preoperculum unarmed. The suboperculum and interoperculum 

 have moderate or rudimentary extended membranous borders. 



The mouth is moderately oblique and never subvertical. The lower jaw 

 is prominent. 



The membranous fold between the limb of the lower jaw is small or rudi- 

 mentary and only developed anteriorly. 



The dorsal fin is much elongated, but commences far from the nape, and is 

 as short as, or shorter than, the anal. It arises behind the vertical of the 

 anus. 



The anal fin is very elongated. 



The ventral fins are approximated, and each has three simply articulated 

 rays. 



This group is very closely related to the Dactyloscopinas, but differs so much 

 in the form of the head that its affinities at first might well be overlooked. 



Genus MYXODAGNUS Gill. 



The body is quite slender, the greatest height being contained about ten 

 times in the length, 



1861.] 



