352 TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



The skull of one of these symbranchids, Monopterus javanensis, has been described and 

 figured both by Boulenger (1910, pp. 597-598) and Tate Regan (1912c, pp. 388-390). 

 Our figure (Fig. 231), however, represents a skull of the allied genus Symbranchus. This 

 type of skull is very long and narrow, mostly in the interorbital region. In some ways it is 

 strongly suggestive of the skull of the so-called electric eel {Electrophorus), an interesting 

 example of convergence. The cranial table consists largely of two wide flat parietals which 

 meet in the mid-line above the minute supraoccipital. This arrangement, as in so many 

 other cases, appears to be correlated with a long flat-topped skull in which the axial muscles 

 do not extend on top of the occiput. 



All the vertical diameters are reduced so that the braincase appears like a long, gently 

 tapering tube in side view. The middle part of this tube is formed by a long descending 

 flange of the frontal which has a long contact with the stout parasphenoid. On the whole, 

 this part of the cranium rather suggests modern amphibian skulls with elongate spheneth- 

 moid bones, — another case of convergence. 



The jaws in this fish are fairly long, although the suspensorium is inclined forward. 

 The premaxillae, thickened in front, are elongate and slender posteriorly; they are appressed 

 to the maxilla, which is rod-like anteriorly and wider posteriorly. The premaxillas bear 

 very short, recurved, conical teeth; the dentary, very delicate, minute, recurved teeth. The 

 rear part of the mandible is disproportionately large with strong ascending or coronoid 

 process. There is a crescentic band or series of small teeth on the palatines and pterygoids. 

 The palatines, according to Tate Regan (1912f, p. 389), meet below the vomer and lack 

 maxillary processes — an unusual arrangement. The mesopterygoid is absent and the 

 ectopterygoid enlarged. The opercular is reduced to a rather small, downwardly-directed 

 spatulate piece bearing a tab-like subopercular. The interopercular is a. broad, short, 

 curved slat. The curved preopercular covers the forwardly-directed suspensorium in the 

 usual manner. Several elements of the normal fish skull have disappeared, including the 

 maxillary process of the palatine, the mesopterygoid, the basisphenoid, alisphenoid, orbito- 

 sphenoid, opisthotic, suborbitals (Regan, 1912c, pp. 388, 389). Thus this skull abounds in 

 convergent resemblances to skulls of characin-eels and true eels, but evidently represents 

 a quite different stock. 



On the coasts of Australia and Tasmania are found small, eel-like fishes known as 

 "shore-eels" {Alahes or Chilobranchus) but which Boulenger and Tate Regan refer to the 

 order Symbranchii. Their external similarity to certain eel-like blennioids (Scytalinae and 

 Zoarcidse) is so strong that Vaillant, quoted by Tate Regan (1912c, p. 388), expressed the 

 opinion that they are indeed related with the blennioids rather than with the Symbranchidae, 

 but, according to Tate Regan, ALabes "in its osteology differs widely from the Blennioids, 

 and although it also differs suflRciently from the Symbranchoids to be made the type of a 

 separate suborder, its relationship to them is quite clear." The skull diflfers from that of 

 Monopterus in the extreme shortening of the snout; this makes the skull in top view very 

 short and relatively wide. The premaxillae have a very stout, fairly long ascending process 

 and a very short tooth-bearing branch. The maxilla is a small rod behind the large pre- 

 maxilla; the dentary is short and thick with small erect teeth, the articular short with very 

 strong short coronoid process. All this indicates a "small-mouthed nibbling" habit. The 

 telescoping of the snout has widened the braincase and thrust apart the flat parietal plates, 

 exposing the flattened supraoccipital plate in contact with the frontals. The short para- 

 sphenoid is widely separated from the frontals by the expanded prootics and exoccipitals. 



