MB. J. W. DAYIS ON CHONDBOSTEUS ACIPENSEBOIDES. 611 



bifurcation. A keel extends along the lateral surface of each ray, 

 and a line of pustulations extends along the median surface of the 

 keel. The anterior ray or spine is quite smooth. The fin is 

 capable of wide expansion ; as preserved, the breadth of the outer 

 margin of the fin is equal to the length of the anterior rays. The 

 pectoral fins in this species approach the existing forms in possessing 

 a strong, spinous anterior ray, and, to the same extent, seem to 

 differ from the fossil forms described by Sir Philip Egerton from 

 the same locality. 



The tympanic arch or suspensorium consists of three parts, each of 

 which is represented by a tolerably complete ossification, and together 

 they connect the cranial bones with the mandible. The epitympanic 

 or hyomandibular (23) is the most prominent bone of the series : it 

 is 3'3 inches in length, the articular surface is 1-2 inch across ; it is 

 contracted in the middle, and expands again at its lower extremity to 

 slightly under one inch in breadth. The bone is thick and strong, and 

 has a solid fibrous appearance. Its upper extremity has a double 

 surface for articulation, and was connected with the mastoid, and 

 probably with the postfrontal bone, though the connexion is not 

 quite so clear as that with the mastoid in this specimen. The 

 lower extremity is rounded and thinner than the upper; to it is 

 attached a smaller plate, the mesotympanic or symplectic (31) ; 

 the latter is partially covered by the operculum posteriorly. Its 

 exposed surface is 0*8 inch across ; its lower extremity affords 

 attachment to the hypotympanic or quadrate (26), an ossification of 

 considerable size supporting the posterior extremity of the man- 

 dible, Its form is not readily distinguishable. Its posterior margin 

 is covered by the operculum ; anteriorly its extent is lost amidst 

 several smaller bones which may pertain to the hyoid apparatus. 



The hyoid apparatus is mostly hidden by the bones of the tym- 

 panum and the operculum. Between the suboperculum and the 

 mandible, a distance of 2 or 3 inches, the ccratohyal (38) may- 

 be distinguished, with six short bones attached to it, the latter 

 evidently bearing some relation to the branchiostegal rays (43) ; the 

 posterior ray is one inch in length, those succeeding are shorter, 

 and they also diminish in thickness. The anterior bones of the 

 hyoid arch are obscure. In a cavity above the ceratohyal, bounded 

 by the posterior part of the lower jaw and the hypotympanic, three 

 bones are exhibited ; the exposed parts are 0*2 inch in thickness 

 at the anterior end, decreasing backwards as they sink beneath 

 the superincumbent bones. These osseous rods represent some part 

 of the branchial apparatus, probably the basal portion of the 

 ceratobranchials . 



The mandibles and the maxillaries in this species are large and well 

 ossified ; in this respect differing considerably from the existing species. 

 There is no evidence of teeth, and the inference naturally arises 

 that the fossil, like its recent representatives, was devoid of teeth. 

 The mandible (34) is 4*5 inches in length, to the extent preserved ; 

 but it is probable that a little more must be added, because the bone 

 ends abruptly ; its anterior termination is wanting. The external 



