564 RAMSAY H. TRAQUAIR ON AMBLYPTERTTS, 



upwards and backwards. In front of the lower end of the sub- 

 operculum, a small but very distinct interoperculum is seen, of a 

 triangular shape, with anteriorly directed apex. The praeoperculum, 

 which does not cover any portion of the cheek, shows a distinct 

 upper and lower limb, the upper being nearly perpendicular, and 

 curving round below into the lower, which, passing forwards, carries 

 the articulation of the lower jaw considerably in front of the upper 

 extremity of the suspensorium. The jaws are comparatively feeble, 

 and the mouth very small. The mandible has quite a different shape 

 from that in Palceoniscits, being, of. course, considerably shorter, and 

 seems to form the immediate margin of the mouth only towards its 

 extremity, which is bent a little downwards. The maxilla is 

 especially feeble, extending only to about half the length of the 

 mandible, and is absolutely unlike that in any of the Pakeoniscida?, 

 as it stops short just before the orbit, and ends with a rounded 

 spatulate extremity, which overlaps the mandible considerably in 

 front of the quadrate articulation of the latter. Mr. Kirkby makes 

 no mention of teeth ; nor have I discovered an}^ ; nevertheless it 

 would be hardly safe to conclude that the jaws were edentulous. 

 The branchiostegal ra} T s are few in number, about seven on each 

 side ; the posterior ones are rather long, narrow, and gently curved ; 

 but they become rapidly shorter in front. In one specimen, com- 

 pressed upon its back, a space is seen just behind the symphysis of 

 the mandible, and in front of the branchiostegal rays of each side, 

 which was probably occupied by a large median "jugular" as in 

 Dapedius, Engnathus, &c, and in the recent Amia. The bones of 

 the cranium proper are not well seen, owing to their delicacy, and to 

 the crushing which they have undergone ; the ethmoidal region is 

 usually wanting or undecipherable as to its component parts. The 

 frontals are almost always distinct as two well-marked roof-bones, 

 broader behind than before, their outer margins being excavated in 

 front for the orbits. Two shorter parietals succeed the frontals 

 behind ; and there are evident traces of a squamosal plate on the 

 outer side of each parietal, above the suspensorial articulation, 

 though the operculum is usually crushed down over this region of 

 the skull. There are faint traces of small plates completely 

 surrounding the orbit, which was placed nearly right over the 

 articulation of the lower jaw instead of being considerably in front 

 of it as in Palceoniscits. Traces also of the palatoquadrate arch are 

 seen in many specimens ; but it is hardly possible to make out its 

 constituent bones ; a well-marked quadrate, however, is distinct 

 enough. The direction of the suspensorium is undoubtedly con- 

 siderably forwards as well as downwards. 



Of the elements of the shoulder-girdle, the posttemporal and 

 supraclavicular are so generally covered and obscured by the 

 opercular bones that a description of them is hardly possible. The 

 clavicle, however, is usually well seen, and differs greatly from that 

 in the Palseoniscidae. It is a comparatively slender bone, bent 

 forwards at a very obtuse angle about its middle ; the lower 

 extremity is pointed and comes in contact with its fellow of the 



