Dr. R. H. Traqucair on the Genus Dipterus. 9 



of ordinary Ganoids and Teleostei. Anteriorly, at the broad 

 depressed snout, sutures cease to be traceable in this bony 

 and ganoid covering, which, becoming reflected round the 

 oral margin, forms a rounded upper lip, overhanging the cor- 

 responding mandibular lip when the mouth is closed, as is 

 seen in one specimen in the Hugh-Miller collection. Looking 

 at this lip from the lower aspect of the cranium (PI. III. fig. 1), 

 the reflected bony covering shows on each side two wide 

 notches, anterior and posterior (w and ?i'), which certainly 

 indicate the position of tlie nasal openings and show that these 

 were placed just as in CeratoduSj as has been already pointed 

 out by Dr. Giinther. There is no distinctly differentiated 

 maxilla or j^raimaxilla ; but the cheek is covered by an arrange- 

 ment of bony plates, which encircle the orbit and inferiorly 

 continue the upper margin of the mouth for a little distance 

 backwards from the nasal margin of the snout, these plates 

 being represented in Ceratodus only by the chain of small 

 suborbital ossicles imbedded in the firm fibrous band below 

 the eye*. 



The opercular bones of Dtpterus correspond in number and 

 position with those of Ceratodus^ but differ in being of a broader 

 and rounder shape, and, of course, in having ganoid surfaces. 

 There is a large operculum^ below which there is a much 

 narrower plate corresponding to that bone which in Ceratodus 

 is interpreted by Prof. Huxley as interoperculum ; .but I have 

 seen nothing which can be taken to represent a prgeoperculum, 

 though Pander has figured a plate which he supposed might 

 represent that element. The jtigula?- 2>icites are obvious, and 

 seem to have existed as two pairs, anterior and posterior ; but 

 I have not seen the median plate figured by Pander (o/). cit. 

 tab. 1. figs. 9a, 23). 



The bones of the shoulder-girdle correspond closely with 

 those of Ceratodus. There is a broad supraclavicular, proceed- 

 ing backwards and a little downwards from the posterior part 



* With regard to the suborbitals of Ceratodus, it may here be appropriate 

 to correct a somewhat serious error which occurs in Mr. L. C. Miall's 

 figure of the skull of C. Forsteri (Sireuoid and Crossopt. Ganoids, pi. 1 a. 

 fig. 2). The suborbitals are not figured ; nor are they mentioned in the 

 text ; but the cheek is represented as covered by a large plate of cartilage, 

 in which a circidar hole for the orbit is, as it were, punched out ; and in 

 the explanation to fig. 3 of the same plate (in which the cartilage is 

 represented as cut away to afford a side view of the pala1 o-pterygoid and 

 its dental plate) it is said that '''the lateral cartilages are largely removed." 

 Now this " lateral " circumorbital cartilage (or " cartilages ") simply does 

 not exist ; and I ha^e myself, on the contrary, completely verified Prof. 

 Huxley's statement as to the suborbital fibrous band and osseous chain ; 

 only in my specimen I find five such oasicles, instead of three as given by 

 Prof. Huxlev. 



