354 TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



chambers, long narrow frontals and short parietals, which are well separated by the supraoc- 

 cipital. There is no opisthotic, orbitosphenoid nor basisphenoid; the prootic separates the 

 parasphenoid from the alisphenoid; the prootics are elongate, flanking the narrow parasphe- 

 noid; the palatine is a long narrow lamina which is firmly united to the elongate vomer and 



brsto 



'"' Mastacembelus 



Fig. 233. Mastacembelus. 



is wedged in between the opposite lateral ethmoids. The pterygoid is movably articulated 

 with the lateral ethmoid external to the palatine. The mouth is small and subterminal, 

 teeth villiform on the premaxillse and dentaries, maxillae firmly attached to the nonpro- 

 tractile premaxillse. The hyopalatine and opercular bones are all present (Regan). Gill- 

 cleft inferior (Boulenger), as in the symbranchoids; branchial arches percoid (Regan); 

 posttemporal absent, the pectoral arch suspended from the skull far behind the skull 

 (whence the name Opisthomi). 



Boulenger suggested (1910, p. 716) that this single family is possibly derived from the 

 Blenniidae. Tate Regan, however, concludes (1912^, p. 218) that these fishes "are related 

 to but more specialized than the Percomorphi, but they show no particular affinity to any 

 group of Percomorphous fishes." 



In Mastacembelus armatus, according to Frost (1930i, p. 625), the otolith (sagitta) is 

 of the percid type, except in certain details. No special resemblances to the blennioid types 

 figured by Frost (1929a, PI. I, Figs. 9-19) were noted. 



Ammodytoidei (Sand-lances) 



Another offshoot of the percomorph group which is otherwise incertee sedis is the family 

 of the sand-lances, Ammodytidse. These small sagittiform fishes dart into the sand; 

 perhaps their acutely pointed mandible serves as the point of the lance. The long narrow 

 skull (Fig. 234) presents to my scrutiny no hint of its derivation. There are several very 

 curious features; the end of the mandible bears a unique elevation, which may support a 

 pad of skin in life. The long premaxillse are very slender, much more so than the long 

 maxillae. The proximal end of each of the latter is expanded. The long narrow bars which 

 Thilo (1920) mistook for the ascending processes of the premaxillse are in reality the extremely 

 narrow anterior extensions of the mesethmoid, the true ascending processes of the premaxillse 

 being very small. Hence the fish cannot have a protractile mouth and Thilo's description 



