PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
291 
by Miller iu 1831, introduced by liim to the scientific world in 1839, and named 
Ptenchthys by Agassiz in 1840. 
The aiitlior then proceeded to offer some critical remarks on several of the genera 
and species which Prof. M'Ooy has described from the Old Red Sandstone Chiro- 
lepia velox, M'Coy, is regarded by him as a good species ; but C. curtus as identical 
with C. Cummingice, and C. macrocepJialvs with C. TraUUi. Chiracanthus gran- 
dispimts and C. pulverulentus are regarded as good species ; but C. lateralis is 
referred to C. minor. Diplacanlhus gibbus and D. perarmatus are accepted. The 
substitution of Diploptcrax for Diploptervs is not considered necessary. Diplo- 
plerus gracilis a])pears to be a variety of D. Agassizii. The occurrence of D. 
macrolcpidotus in Caithness, and the restriction of B. maci-ocephalus to Lethen- 
bar anil Russia, are regarded as a reason for not accepting Pro£ M'Coy's view as 
to the identity of these two forms. 
Osttohpis arcnaius, stated by Prof M'Coy to occur at Orkney, has been met 
with only in the Ganirie by Sir Pliilip. 0. brevis is regarded as a good species, 
though the apparent breadth of the head has probably been misunderstood. Hugh 
Miller has well ligiu'cd and described the cranial anatomy of this species in the 
"Footprints." i'riplnpierus Pollexfeni is also considered to be well established 
generically and specifically. Sir Philip coincides with Prof M'Coy in classing 
Diplerus with the Ccetacanthi, but observes that it is distinct from Glyptolepis. 
Dipterus has but one anal fin. Uiptei us brachypygopterus and D. macropygopterua 
are, in the author's opinion, synonyms ; but D. Valenciennesi is regarded by him as 
distinct. 
Conckodm is esteemed by the author only a provisional genus. 
Sir Philip agrees with M'Coy hi separating from the Holoptychius the large 
fishes of the coal-measures which have received the name Rhizodus fiom Prof. 
Owen. The latter have ossified vertebral columns. Ilolopiycliins has decidedly two 
dorsal fins. Some good specimens lately obtained at Dura Den prove that H. 
Andtrtoni and H. Flemingii are specifically the same. The determination of H. 
princeps by scales alone is not regarded as satisfactory ; but JT. Sedgwickii is a 
good species. Gyroptychius angustus and G. diplopteroides are considered as good 
species of a new and important genus ; but Sir Philip refers them to the Sauro- 
dipteridw, not to the Calacanthi. Platygnathus Jamicsoni, Ag., is well founded, 
as proved by recent cUscoveries in Dura Den ; but the specimen of jaw named P. 
paucidens by Agassiz is assigned to Asterolcpis by Hugh Miller. 
With regard to the Placodermata of M'Coy, PtericJtthys and Coccosteus are the 
types, and Chelyophorus is probably a member of the family ; but it is still doubtful 
whether Asterolcpis and Heterosteus belong to it. Cephalaspis, Pteraspis, and 
Auchenaspis remain for the limited Cephalaspidt^. 
PUricliihys had certainly one dorsal and two ventral fins. 
Sir Philip remarks that in Coccostevs M'Coy and others have mistaken for 
vertebral centres the thick lower extremities of the neiu'apophyses ; hence the C. 
microspondylus of jNI'Coy is a misnomer, and what he terms the " dermal bones' of 
the dorsal fin reversed," in his specimen, are the hEemapophyses. Sir Philip thinks 
that C. microspondylus and C. trigonaspis must be regarded as synonyms of C. 
decipiens, Ag. C. 2»isillus is quoted as a good species, and probably 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 un- 
pubUshed letters by the late Hugh Miller, descriptive of stractural characters of 
the Coccosteus. Among these notes is the description of a small well-defined 
Coccostem v,'h\ch Sir Philip proposes to signalize as C. Milleri. [Drawings and 
casts, prepared hj the late Mr. H. Miller, illustrated these supplemental notes.] 
2. " On the \ellow 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 ascenchng order). — 1. Grey sandstone, the 
equivalent of the Carniylie and Forfarsliire flagstones, with Cepihalaspis and 
Pltrygolus. 2. The red and mottled beds, such as those of the Carse of Gowrie, 
and the Clashbmnie zone with Holoptychius nobilissinms, Phyllolepis concentricus, 
and Glyptolepis elegans. 3. Conglomerates, marls, and comstone, with few and 
