612 



ME. J. W. DAVIS ON CHONDROSTEUS ACIPENSEROIDES. 



surface of the jaw is strong and rounded, 0*5 inch in diameter. 

 Posteriorly it becomes thinner and assumes an expanded form ; the 

 inferior margin is also rounded, whilst the superior extremity is 

 produced to form a styliform process extending backward quite 

 half an inch. It was, probably by this process that the man- 

 dibular bone was connected with the quadrate or hypotympanic, 

 with which it is in close proximity. The part preserved may 

 be equivalent to the dentary element in the lower jaw of the 

 Teleosteans ; and the posterior articular portion which connected 

 the jaw with the hypot} T mpanic, in this specimen defective, 

 may have been mostly cartilaginous, with a thin osseous struc- 

 ture, of which there is a trace extending over the ceratobran- 

 chials. The maxillary bone (18) is large and crescentic in outline ; 

 its anterior portion, like that of the mandible, is thicker and 

 stronger than the posterior. It commences in front in connexion 

 with the premaxillary ; the upper margin of the former is overlain 

 by the lower portion of the latter. The total length of the maxilla, 

 allowing for its curvature, is 4*5 inches ; its height at the anterior 

 part is 0'5 inch. The upper surface is deeply concave, the lower 

 one angular ; the depth at 2*0 inches from the anterior extremity is 

 increased to 1*0 inch ; thence it decreases towards the upper 

 posterior extremity to 0*35 inch about half an inch from the end. 

 The latter again expands and is more or less rounded. 



The posterior expansion of a large bone midway between the 

 orbit and the maxilla is the palatine (22). It is 1*3 inch in 

 breadth, the length of the part preserved is 2*0 inches. It has 

 a fibrous structure radiating from the anterior extremity of the 

 broken bone. Its posterior margin is rounded, the anterior part 

 is constricted to 1*0 inch in breadth. The remaining part of the 

 bone has disappeared with the whole of the anterior extremity of 

 the head, by the loss of a portion of the slab on which the fossil is 

 exposed. The posterior margin of the palatine is in close contact 

 with the tympanic elements and with the posterior extremity 

 of the upper jaw. Between the palatine and the epitympanic bone 

 there are a few small bones or fragments, of an indefinite character, 

 which cannot be localized with any amount of certainty. 



Osseous neurapophyses are preserved in the anterior portion 

 of the bocly. There is no trace of the vertebral column nor 

 of ribs or hsemapophyses, except in the caudal fin, where haemapo- 

 physes support the lower lobe, as will be mentioned hereafter. 

 The neurapophyses extend from the occipital region of the skull, 

 situated high in the body, to the base of the dorsal fin, a length of 

 13*0 inches. In this length there are preserved 35 neurapophyses 

 representing the same number of vertebrae. The first ray of the 

 dorsal fin is inserted above the 30th vertebra. The total number of 

 vertebrae comprised in the spinal column would in all probability be 

 from 80 to 85. The anterior neurapophyses are 0*7 inch in length, 

 divided at the base for the passage of the spinal cord, somewhat 

 constricted mesially, and expanded at the upper extremity to afford 

 attachment to a second series of interspinous bones, 1-25 inch in 



