Structure of Coccosteus decipieng, Agassiz. 131 



turns sharply forwards, passes on to the anterior part of the 

 preorbital 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 con- 

 spicuous 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 postorbital, and passing along as a suborbital branch 

 close to the hollo wed-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 

 Museum shows evidence of a sclerotic ring such as has been 

 figured by v. Koenen (10, pi. ii. fig. 2, pi. iv. fig. 2). 



Internal Skeleton. — In the typical Coccosteus decipiens, 

 Ag., there is no trace of vertebral centra, the space occupied 

 by the persistent notochord being always empty in the fossils. 

 Agassiz in his restored figure (I, pi. vi. fig. 3) has repre- 

 sented on both dorsal and ventral aspects of the notochordal 

 space a continuous row of distally-pointed neurapophyses and 

 hajmapophyses, also a dorsal and anal fin situated opposite 

 each other, each supported in Teleostean fashion by a series 

 of proximally-pointed interspinous bones, dipping down be- 

 tween the neurapophyses, the supposed fin-rays being, accord- 

 ing to the same idea, pointed at their extremities. Pander (6, 

 pi. iv. fig. 1) still retains the two median fins, with the long 

 liEemapophyses in front of the anal, though he was more 

 correct in making the interspinous bones articulate end to end 

 with the neurapophyses by expanded extremities. But though 

 M'Coy had previously (5, p. 602) strongly doubted the exist- 

 ence of an anal fin in Coccosteus, Pander's figure has been copied 

 into almost every text-book; Prof, von Koenen has trans- 

 ferred the body-skeleton and fins as there represented to his 

 restoration of the allied genus Brachydeirus, while the anal 

 fin is also mentioned as present by Zittel in his handbook (14, 

 p. 160). M'Coy was, however, correct — there is no anal fin 

 in Coccosteus ; but besides this Pander's figure is incorrect in 

 other points, which I shall now indicate. 



It is not possible to trace the vertebral column to its com- 

 mencement, owing to its obscuration by the dorso-lateral 

 cuirass ; where it first becomes visible is about the middle of 

 the length of the great median dorsal plate. There we find 

 short broad neural pieces continued obliquely backwards and 

 upwards into neural spines, which gradually lengthen until 

 we come to the dorsal fin, which commences a little beyond 



