484 Dr. R. H. Traquair on Fossil Fishes 
nomenclature of the fishes of the Old Red Sandstone I stated 
that I had never convinced myself of the occurrence of this 
species in Caithness at all ; and there can be no doubt that 
the Thursius macrolepidotus (Sedgw. & Murch.) of the 
Thurso beds has often been mistaken for it. From Achan- 
arras, however, two specimens — one in the Edinburgh 
Museum, the other in my own collection — are undoubtedly 
referable to Osteolepis macrolepidotus , Ag., which may be 
easily distinguished from the smaller 0 . microlepidotus , 
Pander, by the more oblong form of the cephalic shield and 
the more acute angle formed by a Y-shaped sensory groove 
immediately behind the pineal foramen. 0 . macrolepidotus 
is the species characteristic both of the Orkney flags and of 
the Moray-Firth nodules. 
11. Diplopterus Agassizii, Traill. — In Mr. Edwards's collec- 
tion, at present exhibited in the Owens College Museum, 
there is a specimen of Diplopterus Aqassizii evidently from 
Achanarras. It is merely an impression of a fish lying upon 
its back, yet shows at least one point of interest. 
In a paper on Megalichthys published some years ago I 
stated that u Although omitted in Miller’s and Pander’s 
figures lateral jugular plates are undoubtedly present in 
Osteolepis and Diplopterus as well as in Megalichthys ” 
In no specimen of Diplopterus have I seen the lateral 
jugulars better marked than in the one here referred to, the 
Fig. 3. 
Under surface of the head of Diplopterus Agassizii, reduced one third. 
m.n ., mandible ; Lop., interoperculum ; j. 7 principal j ugular ; m.j., median 
jugular ; l.j. 7 lateral jugular plates. 
head of which I have represented in outline in fig. 3. Here 
it will be seen that they are not symmetrical on the two sides, 
* Geol. Mag. (3), vol. i. 1884, p. 117. 
