124 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 18, 



Age, sex, condition, shrinkage, and compression may each and all 

 affect individuals to a certain extent ; great caution is therefore 

 requisite in estimating the value of such variations. On examin- 

 ing an extensive series of any genus of Devonian fishes, transitional 

 forms are found connecting the more slender individuals with those 

 of grosser proportions, and thus filling up the gap which would be 

 very perceptible if the extreme forms only were examined. This is 

 the case in the genus under consideration ; and having before me such 

 a gradation of forms in Diplopterus Agassizi, I cannot but associate 

 Diplopterus gracilis with that species. 



Diplopterus macrolepidotus. — Prof. M'Coy seeks to substitute 

 this name for Diplopterus macrocephalus of Agassiz. He states that, 

 on examining the original specimens of Dipterus macrolepidotus 

 (Sedg. & Murch.), he finds them identical with Diplopterus macro- 

 cephalus, subsequently described by Agassiz; he therefore asso- 

 ciates the generic title of the latter author with the specific appel- 

 lation of the former. On referring to the original memoir and 

 figures of Sedgwick and Murchison (Geol. Journ. 2nd ser. vol. iii. 

 p. 143, pi. 16. figs. 4, 5), I find that the specimens named "pro- 

 visionally' 1 '' Dipterus macrolepidotus are derived from the Caithness 

 flags. Now Diplopterus macrocephalus has never been found in that 

 locality, but is restricted to the Lethen Bar beds and some Russian 

 deposits ; consequently the alteration cannot be admitted. 



Osteolepis aeenattjs. — This species is stated to be not uncommon 

 in the Old Red Sandstone of Orkney. The only specimens I have 

 met with are from the Gamrie beds, where it is of frequent occur- 

 rence. 



Osteolepis brevis. — There is a small species of Osteolepis not 

 uncommon in the Orkney deposits, which may well be called by this 

 name. 1 have never met with a specimen so large as the one figured 

 by Prof. M'Coy ; but in other respects those I have seen appear 

 to belong to this species. Some of the characters he assigns to it 

 are, however, deceptive, especially the large size of the head. He 

 remarks truly that the specimens are generally crushed vertically, 

 but he explains this by the great width of the head ; I should 

 rather say that the great apparent width of the head is in con- 

 sequence of the vertical crush. It was this species that afforded 

 Hugh Miller the opportunity of making out in such minute detail 

 the cranial anatomy of the genus ; and a reference to his figures, 

 pages 53 and 56 of the ' Footprints,' will show what the true pro- 

 portions of the head are. It is the upcast of the opercular flap 

 and the divergence of the premaxillary bones that give the " very 

 obtusely rounded, nearly semicircular, depressed" character to the 

 head in the figure given at pi. 2 D. fig. 4 of the Professor's work 

 on the Palseozoic Fossils. 



Triplopterds Pollexfjeni. — One of the most constant characters 

 of the Saurodipteridoe being the occurrence of two dorsal fins and 

 two anal fins, the proposed genus Triplopterus, having only one 

 dorsal fin, is a remarkable exception. The general shape of the body 

 and head, as remarked by Prof. M'Coy, and the scale -characters 



