no NEW YORK STATE MUSEUM 



middle line of the inferior-posterior border, a wide, upward excavation, look- 

 ing backwards and downwards. It rapidly contracts into a groove with an 

 angular superior middle line. Whether this groove is part of a tube can 

 not be ascertained, owing to the loss of the bony tissue on each side and 

 below, but it may be only the apical angle of a roof-shaped space, whose 

 lateral slopes are produced on each side, sloping well downwards and out- 

 wards. These sloping faces of the matrix represent a pair of osseous plates, 

 which descended on each side from the sheath of the myelon and chorda dor- 

 salis, for the latter occupied this position in the groove already described. 

 Such a structure would indicate the presence of a number of fixed vertebral 

 elements, such as exists in the chimaeras, the rays, and the sturgeons. . . . 

 At the point of junction of the parasphenoid with the lateral alae of 

 the axis is situated what I suppose to be the foramen magnum. It is the 

 direct continuation of the groove already described, and, being floored by 

 the parasphenoid, has a triangular section. There is no trace here of a 

 fossa for the chorda dorsalis, nor of an occipital condyle, nor is it probable 

 that either existed at this point. The parasphenoid is thin, and there are 

 no indications of teeth to be observed on it. 



It remains for us to state that the thin, vaulted and backwardly curved 

 partition which closed the so called "cerebral chamber" in front is in reality 

 nothing more nor less than the posterior wall of the chondrocranium. It is 

 proved to be such by the notochordal opening above described ; by its form 

 and position, which are extremely suggestive of Dipterus ; ' and by its sus- 

 pension from the cranial roof in a manner recalling that in Neoceratodus. 

 It was, however, but slightly ossified, the bone substance being everywhere 

 thin, and no distinct exoccipital plates being formed about the foramen mag- 

 num. Nothing can be stated of the lateral walls of the chondrocranium, 

 for the reason that they have not been observed in any specimen yet dis- 

 covered ; and it is quite likely that they were unossified. Appearances in 

 Chelyophorus and Homosteus lead us to anticipate that further details may 

 be forthcoming in regard to the chondrocranium and parachordal cartilages 

 than is possible to learn from the less ossified condition of these parts in 

 Macropetalichthys. 



Abdominal armoring. Neither in this nor other species of Macropet- 

 alichthys, nor in the allied genus Asterosteus, have plates been found in 



'Traquair, R. H. On the genera Dipterus, Palaedaphus, etc. Ann. Mag. Nat. 

 Hist. ser. 5. 1878. 2:5, pi. 3, fig. i. 



