470 



DR. W. G. BIDEWOOD ON THE CRANIAL [DeC. 13, 



membranou.s, but partly formed by lamellar extensions of the 

 supraoccipital, epiotic, and sqxiamosal bones. 



There is an auditory fenestra between the pro-otic, exoccipital, 

 and basioccipital. A large osseous bulla, enclosing a terminal 

 vesicle of the swim-bladder, occurs in the pro-otic, and another 

 in the squamosal. The bony envelopes of the horizontal and 

 posterior vertical semicircular canals are very prominent ; the 

 former is conspicuovis on the hinder part of the squamosal biiUa, 

 the latter forms the posterior vertical edge of the epiotic and 

 exoccipital. The posterior depression lying to the mesial side of 

 this edge is rather deep. A small opisthotic bone is present. 

 The supraoccipital has no ci'est and separates the two parietal 

 bones. 



The posterior third of the length of the parasphenoid consists 

 of a pair of parallel laminae bounding the sides of the eye-muscle 

 canal. A process of the alisphenoid runs along the basal portion 

 of the anterior edge of the postfrontal spine, which is not the 

 case in Clupea. A basisphenoid is present, but it has no vertical 

 part descending towards the parasphenoid. The orbitosphenoid 

 is produced foi-ward to meet the back of the combined prefrontals. 

 The vomer is strap-shaped and bears a long median row of teeth 

 which Valenciennes (Hist. Nat. Poiss. xx. 1847, p. 468) failed to 

 notice. There is no dorsal fontanelle between the mesethmoid 

 and the frontals. 



Text -fig. 131. 

 if 



lwv,_ 



topc- 



JTWC 



sop 



pop iop enp 



Bussumieria acuta, right side of skull. For explanation of lettering see p. 493. 



Temporal and Preopercidar Series (text-fig. 131). — The post- 

 temporal has a long limb resting upon the epiotic prominence, a 

 shortei-, i-od-like limb attached to the back of the opisthotic, and 



