(48) 



is not exactly as originally counted in Elassoma zonatum. This last count is 

 however correct, while the first, being made without the assistance of a mi- 

 croscope, may be erroneous. It is best to consider the Illinois, Arkansas 

 and Texas specimens as identical, at least at present. 



Fin formula. Dorsal IV, 10, rarely IV 9. Ventrals, I, 5, Anal 

 III, 5, branchiostegals 5, vertebrae 28. Teeth in lower jaw stout, con- 

 ical, slightly curved, their length about half the depth of the dentary bone ; 

 these teeth, for a part of the way at least, in 2 to 4 rows ; similar teeth on 

 the premaxillaries in 2 or 3 rows ; no teeth on vomer or palatine or on 

 pterygoids ; lower pharyngeals narrow, apparently exactly as in Aplwdoderus, 

 some what triangular, not united, with a few conic teeth, very sharp and 

 slender ; gill rakers small and short, tubercle-like ; nostrils double, close 

 together ; opercular bones and preorbital not serrated. Scales cycloid ; 

 about eleven deep furrows on the imbedded part of each ; concentric 

 strige strong. No lateral line. Vent normal. 



The Elassomatidse then differ from the A2yhododeridse in the position of 

 the vent, in the dentition, {Ajjhododeridae having teeth on the vomer, pala- 

 tine and pterygoids,) in the number of ventral rays, and in the want of serra- 

 tures to the preoperculum and preorbital, the edges of those bones being 

 pectinated in the Pirate Perches. 



Family APHODODERIDuE, (the Pirate Perches.) 

 Genus APHODODERUS, Le Sueur. 



50. Aphododerus isolepis (Nelson) Jordan. Western Pirate Perch. 



(M. V. 249; Sfemotretma isolepis Nelson, 39. j 



This species is very closely related to the eastern A. sat/anus, but 

 apparently differs in the smaller scales and the presence of but three dor- 

 sal spines. The other has more frequently four spines, but often only 

 three are developed. The scale formula of A. isolepis is subject to some 

 variation. The following is the count of the number of scales in longi- 

 tudinal series in ten specimens : 48, 48, 50, 50, 50, 51, 53, 53, 54, 55. 



A study of the position of the vent in A. isolepis has developed some 

 singular things. It becomes evident from the examination of a large series 

 that the position of the vent is not a character of generic importance, as 

 was supposed when the genus Sternotremia was proposed, nor is it appa- 

 rently an individual or a sexual character as has been since suggested. 

 The observations of Professor Forbes, verified by myself, appear to show 

 that the position of the vent is dependent on the age of the fish. In the 

 adult the vent is jugular, close behind the little projecting knob at the 

 throat. In the youngest specimens examined, it is more or less behind the 

 ventral fins. In specimens intermediate in size, its position is intermediate, 

 the degree of advancement being proportionate to the size of the fish. 



Occasional irregularities occur, but the above rule holds so generally 

 that it can not be merely accidental. From it I infer that in the very young 

 the position of the vent will be found to be as usual in Percoid fishes; as in 

 the young flounder the eyes are symmetrical, but as the fish grows older, its 

 aberrant characters become developed. 



