6 Dr. R. H. Traquair on the Genus Dipterus. 



every thine/ else has also been removed, save the two palato- 

 pterygoid ph\tes, which are left still adhering to the under 

 surface of the external buckler. In fact we have here before 

 us as nearly as possible a counterpart in bone of the suspen- 

 sorial portion of the cranial cartilage of Ceratodus ; and that 

 the one was as inseparable a part of the skull as the other is 

 evident on the face of things, even although it is naturally 

 impossible to demonstrate any continuity of original cartilage 

 in the fossil skull. 



The suspensorium of Dipterus is therefore autostylic, and 

 closely resembles in form and relations that of Ceratodus^ 

 from which it mainly differs in being so extensively ossified. 



A comparison of Pander's figures 12 and 13 on plate iii. 

 of his work with a series of well-preserved specimens 

 shows that, misled by accidental fractures, he has dismem- 

 bered the quadrate of Dipterus into two parts, which he 

 calls respectively " pterygoideum externum " and " quadrato- 

 jugale." 



In perfect harmony with the condition of the suspensorium we 

 also find that of the palato-pterygoid plates [pt^ PI. III. fig. 1). 

 Their relations to each other and to the base of the skull are 

 precisely the same as in Ceratodus ; and in their external form 

 they are also very similar to those of that living genus. 

 Their anterior portions, bearing the dental plates, are firmly 

 sutured to each other in the middle line ; their hinder portions 

 diverge backwards and outwards, separated by the anterior 

 part of the parasphenoid, with which they are also immo- 

 vably articulated ; their posterior extremities overlap the lower 

 aspect of the quadrate. In the skull represented in fig. 1 a 

 slight twist, which the specimen has undergone through 

 crushing, has dislocated the left palato-pterygoid a little back- 

 wards and inwards from its position with respect to the 

 quadrate ; but its connexions with its fellow and with the 

 parasphenoid have remained as firm as ever. 



By Pander each palato-pterygoid is represented as con- 

 sisting of two portions, " os palatinum " and " os ptery- 

 goideum internum," separated by a longitudinal suture or 

 groove; and this or a similar statement has been frequently made 

 by otherwriters,whohavefoundin the supposed suture or groove 

 a point in Avhich Dipterus differs as well from the Carboniferous 

 Ctenodus as from Ceratodus^. The examination, however, of 



* Hancock and Atthey, Ann. & Mog. Nat. Hist. (4) vii. 1871, pp. 

 190-198; GUnther, Phil. Trans. 1871, p. 55G ; W. J. Earkas "On 

 the Dentary, Articular, and Ptevygo-palatine Bones of Ctemxhis" Proc. 

 Rov. Soc. of New South Wales, 187G ; Miall, Quart. Journ. Geol. Soc. 

 Dec. 187-4, p. 774. 



