8 



TILE GEOLOGIST. 



be detected. Bound the back of the counterpart cavity, in the op- 

 posing slab of stone, a portion of the transverse section of the back 

 of the skull, showing the bony intercerebral ridge, is to be met with. 



There is near this space a conch oidal fracture, which Mr. Blake 

 thinks might be the impression of the parietal and frontal bones ; but 

 although we believe these bones were within the region of this space, 

 we think the conchoidal fracture has been produced by artificial 

 means. The proximity of these cerebral and cranial relics to one of 

 the missing pieces of stone, renders it highly desirable that some 

 pains should be taken to obtain it, as the beak of the bird's head 

 would have probably projected upwards and inwards into it, as it 

 covered the brain in the slab containing the chief remains. That is 

 to say, the Archseopteryx's head would have rested on its back on 

 the mud, with possibly one or two of the cervical vertebrse attached 

 to it, the beak thus projecting directly upwards, exactly as we usually 

 find those of dead gulls and other birds on our present shores. 



This evidence goes far to support the admirable inferences of Pro- 

 fessor Owen, as the fossil brain presents true bird's characters, and 

 can thus be perfectly distinguished from the very peculiar form of 

 brain in reptiles. 



Explanation of Plate I. 



c, costse ; sc, scapula; h, humerus ; u, ulna ; r, radiu3 ; cr, carpals ; i, ilium ;f, femur ; 

 t, tibia ; wt, metatarsus ; p, phalanges ; ca, cauda (tail) ; &, fossil brain ; a, acetabulum ; 

 1 and 2, carpal hooks, 



ON DIDYMODON* A NEW GENUS OE MINUTE AE- 

 TIODACTYLE MAMMALIA, EEOM THE EOCENE OF 

 VAUCLUSE. 



By Charles Caetee Blake, Esq., 



Lecturer on Zoology at the London Institution. 



Since the original foundation of the genus Dichobune by Cuvier,f 

 and the critical observations made thereon by Owen,J the national 

 collection has continued to receive new accessions, indicating the ex- 

 istence of a certain range of variation in the molars of that genus. 



The specimen (No. 30673) in the British Museum collection, is 

 figured in Plate II., by Mr. Mackie. It consists of the three molars 

 of the right side of a species of small quadruped closely resembling 

 Dichobune. The length of the fractured ramus containing these 

 teeth, of which the inner aspect is exposed to the observer, mea- 



* From SiSu/xo?, twofold, and odovs, tooth. 

 f 'Ossemcns Fossiles, 3 vol. v., passim. 



X Quarterly Journal of the Geological Society, vol. xiii. 1857, p. 254. 



