MYXIXIDAE. 



117 



muscles ; intestine without spiral valve ; gall bladder present ; egg large 

 with horny case provided with threads for adhesion ; marine in temperate 

 regions of both hemispheres. Myxine L., hag-fish, with six pairs of bran- 

 chial sacs opening by one external opening on each side. Bdellostoma 

 J. Mull. (Homea Fleming), with six or more (up to fourteen) branchial 



FIG. 63. Palaeospondylus gunni ventral view of head and side 

 view of vertebral column. tp trabeculo-palatine part of 

 skull ; pa, parachordal part of skull ; d c, Ic, vc oral cirri ; a, b, c, 

 n markings of more uncertain significance ; x post occipital 

 plates (from S. Woodward). 



apertures on each side, each leading to a branchial sac ; the number of 

 branchial sacs may be different on the two sides of the body ; southern 

 hemisphere. Palaeospondylus Traquair, from the old Red Sandstone of 

 Scotland, is supposed to be a fossil Marsipobranch with calcified cartila- 

 ginous endoskeleton (Fig. 63). The notochordal sheath appears to have 

 contained rings. 



