450' 



MR. e, TATE REGAN ON THE 



contact with the preeoperculum the latter lies above it. Also 

 the analogous case of PhractolcEmus may be quoted ; in that 

 geniis the very large interoperculum transmits the sensory canal, 

 but it is the horizontal limb of the praeoperculvim that is lacking, 

 whereas in Lejndosteus the vertical limb has gone. 



The operculum articulates with a knob on the hyomandibular, 

 the suboperculum is well developed, and there are 3 branchio- 

 stegal rays. 



Text-figure 5. 



Lepidosteus platystomus. ■ . • 



A. Prasmaxillary, maxillary, circumorbital, and clieek bones. 



B. Paluto-quadi-ate (outer view). 



pal. palatine; eot. ectopterj'goid (showing groove for attaclimenfr of 

 maxillary) ; ent. entopterygoid ; int. metapterygoid ; q. quadrate. 



C. Opercular bones, etc. 



Tim. hyomandibular ; s?/. symplectic ; op. operculum ; sop. suboperculum; 

 iop. interoperculum ; pop. prseoperculum. 



D. E. Lower jaw, outer and inner aspects. 



den. dentary ; an. angular ; san. supra-angular ; ar. articulars ; par. prse- 

 articular ; id. intra-dentaries. 



The hyoid arch comprises the hj'omandibular, which articulates 

 with the sphenotic and pterotic, the symplectic, which is firmly 

 attached below to the prseoperculum but is remote from the 

 quadrate, the interhyal, the ceratohyal, the hypohyal, and a 

 median basihyal. The ceratohyal has two ossifications, the 

 hypohyal only one. The upper ossification in the ceratohyal is 

 generally termed " epihyal ; " this is certainly wrong, and I 



