Fossil Fishes of the Upper Karroo Beds of South Africa. 255 



supratemporal ossicles, which he describes as follows (7, p. 83) : 

 " Between the posterior margin of the cranial shield and the 

 post-temporal element of the shoulder girdle we obtain a good 

 view of the supratemporal chain of ossicles so seldom seen in a 

 Palaeoniscid head. Of these three are shown, namely, two belonging 

 to the left, and one . . . belonging to the right side of the head ; 

 while traversing all these three we observe an elevated line showing 

 the course of the supratemporal slime canal, which here, as in the 

 salmon and many other fishes, forms a transverse commissure 

 between the right and left main canals." These observations in two 

 different Palseoniscids are extremely interesting in connection with 

 the somewhat similar but different condition in Helichthys. 



In Helichthys, behind the parietals are a pair of large supra- 

 temporals which have a long median suture, and behind these a 

 second pair of supratemporals, small and narrow, and wedged in 

 between the large supratemporals in front and the post-temporals 

 behind. The commissural sensory canal lies entirely in these 

 second small supratemporals. Along the outer side of the parietal 

 and the large supratemporal and in front of the anterior end of the 

 small supratemporal lies the large squamosal, along the middle of 

 which is continued the sensory canal from the small supratemporal. 

 In front of the squamosal are apparently a number of orbital ossicles 

 not satisfactorily preserved, and the sensory canal a little in front of 

 the squamosal bends abruptly down and passes through the ossicles 

 behind the eye. Further it cannot be traced. 



Below the squamosal is a moderately large triangular bone pre- 

 sumably corresponding to the bone marked x in Traquair's figure of 

 the head of Elonichthys and called an accessory piece. Below this 

 triangular bone is a large preopercular, and adjoining this latter in 

 front and below is the maxilla, which is fairly long and slender in 

 front and bears a large number of small teeth. The dentary is long 

 and bears many small teeth, which are arranged irregularly on the 

 upper and inner margin of the bone. 



The operculum is an oblong bone situated below the squamosal 

 and the smaller supratemporal. Below it is the large interopercular, 

 followed by the branchials. These latter are not well preserved in 

 any of the specimens examined. The first three or four are well 

 seen in the type, but the others appear always to lie inside of the 

 mandible, and are thus hidden. 



Most of the surface bones of the head are ornamented, but the 

 details of the sculpturing differ in different specimens. The mandible 

 has on the front part of the lower two-thirds of the outer side a large 



