20 ARKIV FÖR ZOOLOGI. BAND 10. N:0 8. 



A study of sectioiis of a specimen 18 mm. in length shows 

 that tliere are no hony elements ihe developement of which is 

 related to so-called mucous canals. 



Diodoiitidae. 



To judge from the literature the skull of the Diodontids 

 seems in all general eharacters to agree with that of the 

 Tetrodontids. Klein, however, asserts the presence of alisphe- 

 noids. 



Ostraciontidae. 



The skull of the Ostraciontids has been dealt with by 

 HoLLARD and Klein. I have examined a specimen of Lac- 

 tophrys trigonus. 



Supraoccipitale without spina. The lateral occipitals reach 

 each other in the dorsal median line. Basioccipitale, parie- 

 tale, frontale, squamos%im, sphenoticum and prooticum are de- 

 veloped. The fr ont als are paired. Supraethmoideu7n with a 

 large anterior articular surface. Basisphenoideum cannot be 

 distinguished. Parasphenoidenm and alisphenoideum present. 

 Ethmoideum laterale, palatiniim (very small), ectopterygoideum^ 

 metapterygoideum, guadratum, symplecticum (not reaching hyo- 

 mandib.) and hyomandibulare are developed. Vomer is not 

 distinctly marked off from supraethmoideum. It is provided 

 on each side with an articular surface for palatinum. Max- 

 illare and praemaxillare firmly united. Praeopercidum, oper- 

 culu7n, suboperculum and interoperculum (rod-shaped) present. 

 Dentale, articulare and angidare distinct. The last two bones 

 are very small. 



General Remarks on the Skull. 



On comparing the skulls of the different plectognathous 

 fishes with each other, we shall find that, though there are 

 niany differences as to the configuration, several eharacters com- 

 mo7i to all can be recognized. No hones developed in relation 

 to mucous canals. Nasals, suborbitals and opisthoticum are 



