On the Structure o/Coccosteus decipiens, Afjassiz. 217 



seen a curved groove, starting from near the middle of the 

 anterior margin and then curving sliarply round to proceed 

 to the inner border close behind tlie antero-internal angle. 

 On the median dorsal plate a groove is seen of a V-shaped 

 contour, tlie apex being in the middle line somewhat in front 

 of the posterior extremity of the bone, the limbs diverging 

 forwards towards tlie superior margin of the posterior dorso- 

 lateral plate. On the anterior dorso-lateral plate a continua- 

 tion of tliis groove runs forwards to the postero-internal 

 angle of the external occipital, near which it is met by a 

 branch coming diagonally upwards and forwards from the 

 postero-inferior angle of tlie plate. The side-canal thus 

 formed passes now on to the cranial shield at the point 

 indicated, and there at once gives off a branch running 

 forwards and slightly inwards, parallel with and close to the 

 outer margin of the median occipital, becoming lost on the 

 posterior margin of the central. The main groove then runs 

 forwards and outwards parallel with the outer margin of the 

 shield, giving off first a branch passing to the external pro- 

 jecting angle of the marginal plate, then turning forwards 

 and inwards still parallel to the shield-margin it passes on 

 to the post-orbital plate, where it gives off another branch to 

 the post-orbital angle. Here it bends sharply backwards and 

 inwards at an acute angle, runs on to the central plate, 

 approaching its fellow of the opposite side, and near the 

 middle of this plate it again turns sharply forwards, passes 

 on to the anterior part of the pre-orbital, and ends near the 

 small nasal opening in front. In some specimens a cross 

 commissural branch is seen on the central plates, connecting 

 the two main trunks at the conspicuous angles which they 

 make in that place. 



A groove is also observable on the maxilla, apparently 

 continued from the second external branch of the main 

 groove on the post-orbital, and passing along as a sub-orbital 

 branch close to the hoUowed-out orbital margin of the bone. 

 It gives off behind the eye another branch, which passes in 

 a curved manner downwards and backwards towards the 

 margin of the bone posteriorly. 



Sclerotic Ring. — A specimen from Gamrie, in the Edinburgh 



