IN THE PAEAaUATAN LEPIDOSIEEN, ETC. 355 



closely applied to the lateral chondrocranial wall of the mesethmoid region. Perhaps 

 the only other noteworthy feature is the more vertical position which each bone 

 assumes in passing from the distal end of the suspensorial cartilage to the symphysis 

 anteriorly — a peculiarity which evidently owes its explanation to greater forward 

 inclination of the suspensorium itself. 



The opercular and interopercular bones and their cartilaginous vestigial hyoidean 

 rays are essentially similar to those of other Dipnoi, but on the whole are perhaps 

 better developed. 



The three suborbital bones described by Huxley were represented in the specimen 

 examined by myself by four ^ somewhat irregularly-shaped and tubular ossicles which 

 lodged the infraorbital division of the sensory canals of the head. There is a similar 

 but much larger bone situated somewhat above and behind the orbit, articulating 

 internally with the supraorbital margin of the dermal ectethmoid and behind with the 

 lamellar portion of the squamosal, where it is also iu fibrous connection with the 

 hindermost of the infraorbital series. This bone is likewise traversed by a tubular 

 canal, and, as it transmits the supraorbital sensory canal, may perhaps be considered 

 as the remains of a supraorbital series of ossicles. The latter bone is apparently the 

 one figured by Huxley {I. c. fig. 7, p. 37), and by him described as one of the com- 

 ponent elements of the supracranial roof. Tt has also been figured by Miall [22] as a 

 " postorbital " bone. 



The lower jaw is very unlike that of other Dipnoi. It is relatively much more 

 slender and has little more than a rudiment of a coronoid process. The largest bones 

 are those described by Huxley as the splenial and the angular, but while the former 

 is wholly restricted to the inner surface of the ramus, the latter forms the outer surface 

 and extends from the articular extremity nearly to the mental symphysis of the two 

 splenial elements. The two dentary plates described by Huxley are peculiar to 

 Ceratodus. Anteriorly to the symphysis the two Meckelian cartilages unite in a 

 forwardly-projecting concave lamella, regarded by Giinther as representing "lower 

 labial cartilages," but doubtfully so considered by Huxley. There is no trace of the 

 vertically-disposed processes which in Lejndosiren are derived from the Meckelian 

 cartilages and support the folds of mucous membrane projecting into the angles 

 between the mandibular tooth-plates. 



The hyoid arch is much more complete than in any other Dipnoid, and was originally 

 described by Giinther [I. c.) as consisting of a pair of basihyals and a glossohyai. 

 Ridewood [3 5 a] subsequently showed that the paired basihyals are really hypohyals, 

 and the "glossohyai" a true basihyal. In addition to these elements there is also a 

 variously-shaped cartilage attached by ligament to the inner and hinder margin of each 

 suspensorial cartilage, dorsad to the upper extremity of the cerato-hyal, and considered 

 by its discoverer, Huxley {l. c), and also by Gadow (9 a) and Ridewood (I. c), to 

 represent a hyomandibular element. On the authority of Eidewood (/. c.) it would 



' Traquair (37, p. 9) found five suborbital bones in a specimen wliioh he examined. 



