484 



Dr. m. H. Traquair on Fossil Fishes 



nomenclature of the fishes of tlie 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 undoubted! j 

 referable to Osteolepis macrolepidotus ^ Ag., which may be 

 easily distinguished from the smaller 0. microltpidotus^ 

 Pander, by the more oblong form of the cephalic shield and 

 the more acute angle formed by a V-shaped sensory groove 

 immediately behind the pineal foramen. 0. macrolepidotus 

 is the s[)ecie3 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 Mecjaliclithjs published some years ago I 

 stated that "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 ; i.op., iuteroporciiluiu ; /., principixl jugular ; mj., median 



jugular; l.j., lats^ral j ugular 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. 



