Stewart.] Cretaceous Fishes. 289 



so below. Extending backward from above the neural canal 

 there is a somewhat expanded mass of bone which has an artic- 

 ular surface on the front of the arch following. These have a 

 superficial resemblance to the zygapophyses of the higher verte- 

 brates. Just opposite to this on the external side there are two 

 more processes which extend outward and backward. These 

 arc what Professor Hay calls epineurals. 5:: They are largest at 

 the head and become much smaller at the fourth or fifth vertebra, 

 and probably become insignificant or entirely disappear further 

 back. The neural spines of these are directed upward <md ob- 

 liquely backward. 



As we have no well-preserved neural arches farther back than 

 those described above, I will quote Professor Hay's excellent 

 description of the structure of these in the caudal region. 

 Copies of his figures are given on plate XLII. 54 The neural 

 arches here, as elsewhere in this fish, are. connected with the 

 centra by suture, and have usually fallen out before burial, 

 leaving long grooves where their bases were inserted. This was 

 the case with the third vertebra behind the right-hand one 

 shown in fig. 1. When we come to examine the arches more 

 closely, we discover that each lateral half is not a single piece, 

 but consists of two pieces, a basal piece (a, n, a) and the arch 

 proper {n, a). That the proper arch is a distinct piece is 

 shown not only by the existence of a suture, but likewise by 

 the fact that in the vertebra on the left hand of the figure the 

 arch has fallen out of its place before fossilization. The basal 

 or accessory piece is inserted by a shallow gomphosis into the 

 centrum for nearly the whole length of the latter. It rises high 

 in front, and projects so far forward as to come in contact with 

 the basal piece of the next vertebra in front. Behind, the basal 

 piece is directed upward and backward in a rather slender 

 process, which abuts against the anterior edge of the basal 

 piece of the next vertebra behind. It is thus seen that these 

 basal pieces provide the anterior and posterior zygapophyses. 

 They remind us of the articulating processes of certain other 



9a Zool. Bull., vol. If. Ma 1. p. 51. 



54. S / iool. P.iill.. vol. If. No. 1. pp. 47 51. 



