446 Geological Society. 



but Sir Philip refers them to the Saitrodipterida, not to the Ccela- 

 canthi. Platygnathis Jamiesoni, Ag., is well-founded, as proved by 

 recent discoveries in Dura Den: but the specimen of jaw named 

 P. paucidens by Agassiz is assigned to Asterolepis by Hugh Miller. 



With regard to the Placodermata of M'Coy, Pterichthys and Coc- 

 costeus are the types, and Chelyophorus is probably a member of the 

 family ; but it is still doubtful whether Asterolepis and Heterosteus 

 belong to it. Cephalaspis, Pteraspis, and Auchenaspis remain for the 

 limited Cepkalaspidce. 



Pterichthys had certainly one dorsal, and two ventral fins. 



Sir Philip remarks that in Coccosteus M'Coy and others have mis- 

 taken for vertebral centres the thick lower extremities of the neur- 

 apophyses ; hence the C. microspondylus of M'Coy is a misnomer, 

 and what he terms the " dermal bones of the dorsal fin reversed," in 

 his specimen, are the hsemapophyses. Sir Philip thinks that C. 

 microspondylus and C. trigonaspis must be regarded as synonyms of 

 C. decipiens, Ag. C. pusillus is quoted as a good species, and pro- 

 bably the same as one subsequently described by H. Miller as C. 

 minor. 



In a Supplement to this Memoir Sir P. Egerton gives several 

 extracts from unpublished letters by the late Hugh Miller, descrip- 

 tive of structural characters of the Coccosteus. Among these notes 

 is the description of a small well-defined Coccosteus which Sir Philip 

 proposes to signalize as C. Milleri. 



2. . " On the Yellow Sandstone of Dura Den and its Fossil Fishes." 

 By the Rev. John Anderson, D.D., F.G.S. &c. 



In his geological remarks on Dura Den, the author described the 

 sedimentary strata in the vicinity as consisting of (in ascending order) 

 1 . Grey sandstone, the equivalent of the Carraylie and Forfarshire 

 flagstones, with Cephalaspis and Pterygotus. 2. The red and mot- 

 tled beds, such as those of the Carse of Gowrie, and the Clashbennie 

 zone with Holoptychius nobilissitnus, Phyllolepis concentricus, and 

 Glypiolepis elegans. 3. Conglomerates, marls, and cornstone, with 

 few and obscure fossils. 4. The Yellow Sandstone, rich in remains 

 of Holoptychius and other fishes, and about 300 or 400 feet in thick- 

 ness. This sandstone is seen to rest unconforraably on the middle 

 or Clashbennie series of the Old Red at the northern opening of the 

 Den, and at the southern end is unconformably overlaid by the Car- 

 boniferous rocks. It is also exposed beneath the lower coal-series of 

 Cults, the Lomonds, Binnarty and the Cleish Hills. It is seen also 

 in Western Scotland (Renfrewshire and Ayrshire), and also in Ber- 

 wickshire and elsewhere in the ■ south, with its Pterichthyan and 

 Holoptychian fossils. In the author's opinion it is entirely distinct 

 from the " Yellow Sandstone" of the Irish geologists. 



At Dura Den the yellow sandstone in some spots teems with 

 fossil fish, especially in one thin bed. In 1858 a remarkably fine 

 Holoptychius Andersoni was met with ; and this, with many other 

 specimens, fully bears out Agassiz's conjectures for completing the 

 form and details of the fish where his materials had been insufficient. 



