On the Strudure of Coccosteus decipiens, Agassiz. 219 



in the distal, though probably the numbers were equal in the 

 perfect state, and in both sets they have the same form, 

 namely, they are slender, elongated, and expanded at both 

 extremities. It is evident from the last-mentioned circum- 

 stance that the ossicles of the second row are not dermal 

 fin-rays, but belong to the same category as those of the first ; 

 two rows of interspinous bones being, in fact, of constant 

 occurrence in the primitive Ganoids. 



Beyond the dorsal fin the neural spines become very short 

 as well as less oblique in their direction. 



On the haemal aspect of the vertebral axis no such elon- 

 gated apophyses occur anteriorly, as depicted in the restora- 

 tions of Agassiz and Pander. Immediately behind the lateral 

 plates of the cuirass we find small, nearly circular, haemal 

 pieces without spines, then spines are added which, gradually 

 lengthening, become longest in the region opposite the dorsal 

 fin, whence they again diminish towards the extremity of the 

 tail. It is this peculiar lengthening of the ha^mapophyses 

 under the dorsal, a fact also noticed by M'Coy, which has 

 evidently given rise to the old idea of the presence of an 

 anal fin. 



In all specimens of Coccosteus where the internal skeleton 

 is well preserved there is found a pair of peculiar slender 

 bones (x), each of which is pointed at both ends and bent 

 below the middle at an obtuse angle in somewhat L-shaped 

 fashion, the long limb pointing upwards towards the verte- 

 bral axis, the short one forwards. These bones were noticed 

 by Pander (6, p. 73), who, though extremely doubtful as to 

 their nature, supposed that they "vielleicht den Extremitiiten 

 als Stiitzen der weichen Plossen angehorten." Their position 

 is certainly suggestive of their having had something to do 

 with pelvic limbs — more I cannot say. 



Mr A. Smith Woodward has pointed out to me that in 

 several specimens in the British jMuseum a small oval or 

 somewhat rhombic bony plate (;/) is seen lying in a position 

 posterior to the last-mentioned bones. I have not observed 

 it in any other specimens than those ; but its presence in a 

 similar position in more than one example would seem to 

 indicate that it was a scute placed in the ventral mesial line. 



VOL. X. g 



