314 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



membrane bones are included in it is not certain, but it 

 probably represents only the two Meckel's cartilages. 

 From these parts, and the articular elements, a strong 

 tendinous and muscular sheet of tissue passes ventrally 

 and is inserted into the hypohyal elements of the hyoid 

 arch. It is the latter which form the prominent " chin " 

 shewn in fig. 20. 



OPERCULUM 

 PREOPERCULUM 

 SUBOPERCULUM 



HYPO-HYALS\ 



MTEROPERCULUM 



Fig. 22. Malformed skull of Trigla gumardus. Slightly magnified. 



Malformations of this kind are extremely rare among 

 teleostean fishes living in nature. Probably individuals 

 exhibiting them are eliminated at an early stage of their 

 life history. If, as is probably the case, the malforma- 

 tion here described was developed during the post larval 

 stage it is difficult to see how the fish contrived to secure 

 enough food. But it is probable that the gape was of 

 greater extent in this stage, and that the very contracted 

 mouth opening was only developed after adult growth 

 had been attained. 



