218 Proceedings of the Royal Physical Society. 



Museum, shows evidence of a sclerotic ring sucli as has been 

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



Internal Skeleton. — In the typical Coccosteus deci2nens, 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 (1, pi. vi., fig. 3) has repre- 

 sented on botli dorsal and ventral aspects of the notochordal 

 space a continuous row of distally-pointed neurapophyses and 

 hiemapophyses, 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 

 between the neurapophyses, the supposed fin-rays beings 

 according to tlie same idea, pointed at their extremities. 

 Pander (6, pi. iv., fig. 1) still retains the two median fins, 

 with the long haemapophyses 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 thougli M'Coy had previously (5, p. 602) strongly 

 doubted the existence of an anal fin in Coccosteus, Pander's 

 figure has been copied into almost every text-book ; Prof, 

 von Koenen lias transferred tlie body-skeleton and fins as 

 there represented to his restoration of the allied genus 

 Brachydeirits, 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 tlie 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 

 the apex of the plate just mentioned. Here we have two sets 

 of interspinous bones articulated end to end with each other 

 and with the neural spines, which latter are truncated and 

 not pointed. In a very good specimen in the British Museum 

 I count about fifteen ossicles in the proximal set and twelve 



