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360 CEOSSOPTERYGII. 



The ethmoidal region is covered with numerous polygonal 

 ossifications ; and the forward position of the orbit is well 

 shown. The cheek is covered by membrane-bones of which 

 the very large posterior element is distinct ; and immedi- 

 ately below these occurs the long slender maxilla, provided 

 with a series of small teeth. The form and proportions 

 of the operculum and suboperculum are also shown, from 

 the inner aspect, on the left side. Of the fins, the anal 

 and caudal are best preserved ; and a pair of relatively 

 large narrow scales seems to occur in advance both of the 

 first dorsal and the anal. Purchased, 1883. 



28870, P. 716. Imperfect smaller fish, in counterpart ; Gamrie. 



Purchased, 1854, and Egerton Coll. 



P. 4046. Head and portions of trunk of small fish ; Gamrie. 



Purchased, 1883. 



P. 184-5. Two examples of the head with imperfect trunk, the 

 second in counterpart ; Orkney. Purchased, 1881. 



An imperfect scale of an indeterminable genus, from a Lower 

 Palaeozoic boulder near Meseritz, Silesia, is named Gijroptychius 

 posnaniensis, G. Kade, Programm k. Realschule zu Meseritz, 1858, 

 p. 1(5, figs. 6, 7. 



Genus TRISTICHOPTERUS, Egerton. 



[Figs. & Descrips. Brit. Organic Remains (Mem. Geol. Surv. 



1861), dec. x. p. 51.] 



Body much depressed anteriorly, with round or ovoid scales, of 

 which the exposed portion is ornamented with short, antero- 

 posteriorly directed rugae of ganoine. Head-bones more or less 

 tuberculated ; teeth round in section. Ossified ring-shaped ver- 

 tebras in the abdominal region. Anterior dorsal fin opposed to the 

 pelvic pair, and the posterior dorsal to the anal ; tail heterocercal, 

 the caudal fin abruptly truncated posteriorly, having a relatively 

 small upper lobe, and the rays at the extremity of the caudal body- 

 prolongation extending somewhat beyond the others above and 

 below. 



Tristichopterus alatus, Egerton. 



1861. Tristichopterus alatus, Sir P. Egerton, Rep. Brit. Assoc. 1860, 

 Trans. Sect. p. 78, and Figs, and Descrips. Brit. Organic Remains 

 (Mem. Geol. Surv.), dec. x. p. 51, pis. iv., v. 



