tetraodontids, while the other species does not share 

 these similarities. All four species studied are rather sim- 

 ilar externally, with the nasal apparatus about the same 

 in all and varying only in the length of the tube, the up- 

 per lateral line joining the lower, at least a few prickles 

 on the side of the body, and a color pattern featuring at 

 least one large black spot on the side of the body. 



In M. gularis (Dekkers 1975:95, considered gularis a 

 synonym of cutcutia, but the single specimen I have 

 identified and studied as gularis is not conspecific with 

 cutcutia), the sphenotic does not extend laterally beyond 

 the edge of the frontal, the frontal is much expanded lat- 

 erally over the middle of the orbit, the posterolateral 

 region of the jjrefrontal is not much less wide than the 

 average width of the interorbital region, the lateral edge 

 of the prefrontal is gently curved, the ethmoid is very 

 short and relatively wide, the palatine-vomerine strut 

 supporting the upper jaw is relatively short, and the pre- 

 maxillary pedicel is of moderate length (as in most other 

 tetraodontids). 



However, in the other three (leiurus, cutcutia, palem- 

 bangensis) species of Monotreta studied the sphenotics 

 extend laterally beyond the edge of the frontal (at least 

 as much as illustrated for leiurus; in palembangensis the 

 sphenotic is even wider and further extended laterally), 

 the frontal is only moderately laterally expanded over 



Figure 274.— Dorsal views of skulls of: left, 

 Chonerhinos modestus, .54.5 mm SL, Borneo; 

 right. Xenoplerus naritus, 143 mm SL, Bay of 

 Bengal, with the barred band representing the 

 cut surface of the thickened frontal, removed 

 to expose the portions of the sphenotic and 

 pterotic which it overlies (dashed line marks 

 lateral edge of removed portion of frontal). 



the middle of the orbit and is strongly tapered anteriorly 

 to the posterolateral region of the prefrontal, which is 

 much less wide than the average width of the interor- 

 bital region, the lateral edge of the prefrontal is rela- 

 tively straight and produced anterolaterally to a point, 

 the ethmoid is very long and of moderate width, the pal- 

 atine-vomerine strut supporting the upper jaw is long 

 relative to gularis (but not relative to a large number of 

 other tetraodontids), and the premaxillary pedicel is of 

 relatively great length. 



The open space enclosed between the dorsomedial 

 edges of the two premaxillaries in M. leiurus, cutcutia, 

 and palembangensis is much greater than in gularis or 

 any other tetraodontid, partially because of the rela- 

 tively great length of the premaxillary pedicels, but 

 equally important because the open space extends far 

 further forward beyond the level of the anterior ends of 



337 



