210 



IOWA GEOLOGICAL SURVEY 



Family CTENODONTIDAE.* 



Cranial roof bones numerous; no secondary upper jaw, and 

 no marginal series of teeth above or below; jugular plates pres- 

 ent or absent. Dentition consisting of an upper and lower pair 

 of triangular "ctenodont" dental plates, whose outwardly radi- 

 ating ridges usually terminate in rows of conical denticles or 

 tubercles, rarely smooth or nearly so ; no vomerine teeth so far 

 as known. Tail heterocercal or apparently diphycercal. Ex- 

 cluding the anal, which is always distinct, the remaining median 

 fins are either distinct or continuous (two dorsals in all genera 

 but Phaneropleuron). 



Genus DIPTEMS Sedgwick and Murchison. 



Body elongate, not much laterally compressed, covered with 

 enamelled cycloid scales ; head depressed, snout obtuse. Dental 

 plates, above and below, triangular in shape, with outwardly 

 radiating ridges, tuberculated or strongly crenulated, sometimes 

 becoming obsolescent. Paired fins acutely lobate, two remote 

 dorsal fins opposed to the pelvic and anal fins, separated from 

 the caudal. 



Fig. 33. 



Fig. 33. Dipterus valenciennesi Sedgw . & Murch. Lower Old Red Sandstone; Scotland. 

 stored by Dr. R. H. Traquair. x I. (alter Traquair.) 



Left lateral aspect as re 



Our knowledge of the complete form of this genus, shown in 

 text-figure 33, is dependent entirely upon the small, well-pre- 

 served skeletons found in the Scottish Lower Old Eed Sand- 

 stone. These remains were originally described in successive 



*On the propriety of using this term instead of Dipterida?, see Traquair in Geol. 

 Mag. 1893, dec. 3, 10, p. 264. 



