ON CERATODIJS FORSTERI. 147 



The latter has eighteen series of scales, five of which are above 

 and eleven below the lateral line, while the former, with 

 twenty-one series of scales, has six above and thirteen below the 

 lateral line. The skeleton is cartilaginous. Wherever bony 

 tissue appears it is always covering the' cartilage, as for instance, 

 in the skull, where the bony plates entirely cover the cartilage, 

 so that the skull is nothing more than a closed cartilaginous case 

 covered and defended by a bony defence. The muscles of the eye, 

 for instance, pass backwards hetween the bone and the cartilage. 



The spinal column is a true notochord. There are four gills on 

 each side consisting of broad, isolated lamellaB, and attached to 

 the walls of the gill cavity. 



The lung of the Barramanda is simple and sac-like, the interior 

 being divided into compartments by strong septa. 



"When the fish swims in water and breathes by means of the 

 gills, the lung takes the place of the common air bladder. But 

 when the water disappears, or the animal is in the mud, then the 

 gills are useless, and breathing takes place by the lungs, which, 

 like Batrachians, communicate with the upper part of the 

 mouth. 



Por a complete account of the minute anatomy of the Ceratodus 

 the student is referred to Dr. GUnther's paper in Phil, Trans, 

 461, 22, 1872. 



Oar attention is, however, more particularly arrested by the 

 teeth, on account of our familiarity with the fossil ones found at 

 Aust. 



The fossil teeth (pi. 5, fig. 2) at most have five horns only on 

 the outer edge of the dental plate, while the recent ones have 

 six (pi. 4, fig. 3). The grinding surface is beautifully marked 

 with star-like punctuations, which are the terminations of the 

 medullary canals. These canals are parallel to each other, and 

 sometimes dichotomize, but never anastomose. The crown of 

 the tooth is not very thick, and is separated from the other part 

 by an extensive pulp cavity. In the fossils this pulp cavity is 

 nearly obliterated. The horns or prolongations of opposing 



