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ClilM.ttKOlDtil. 



The following species are placed here : — 



Palasomylus crassus : Rhynchodus crassus, J. S. Newberry, Rep. 



Geol. Surv. Ohio, vol. i. pt. ii. (1873), p. 312, pi. xxix. 



fig. 3, and Palaeoz. Fishes N. America (1889), p. 49, pi. 



xxviii. fig. 4. — Corniferous Limestone ; Ohio. [Columbia 



College, New York.] 

 Palceomyhis frangens : Rhynchodus frangens, J. S. Newberry, 



op. cit. (1873), p. 311, pi. xxviii. figs. 2, 3, and op. cit. 



(1889), p. 48, pi. xxix. figs. 2, 3. — Corniferous Limestone; 



Ohio. [Columbia College.] 

 Palceomylns greenei : Rhynchodus greenei, J. S. Newberry, op. cit. 



(1889), p. 51. — Hamilton Group ; Milwaukee, Wisconsin. 



Family SQUALORAIIDtE. 



Body depressed, but elongated. Head produced into a flat ros- 

 trum, without lateral teeth. Dentition consisting of thin, trans- 

 versely curved plates, without differentiated tritoral areas ; a single 

 pair in the lower jaw, meeting at the symphysis, and two pairs in 

 the upper jaw, the hinder pair being closely apposed in the median 

 line anteriorly, but divergent posteriorly. Dorsal fin-spine absent. 

 Males with a prehensile spine upon the snout. 



Genus SQUALORAJA, Riley. 

 [Proc. Geol. Soc. vol. i. 1833, p. 484.] 

 Syn. Spinacorhinus, L. Agassiz, Poiss. Foss., Feuill. 1837, p. 94. 



Rostrum much produced ; tail gradually tapering to a point. 

 [Median fins unknown.] Teeth marked with a series of hard, 

 parallel, longitudinal corrugations ; rostral spine of male slender and 

 pointed, with expanded base and a cluster of large recurved denticles 

 on the inferior aspect near its insertion ; dermal tubercles conical, 

 radiately sculptured, sparsely arranged. Vertebral rings well cal- 

 cified, consisting of several concentric lamellae. 



This genus has hitherto been regarded as a Selachian, though the 

 Chimaeroid resemblance of its rostral region, the supports of its lateral 

 line, &c, have been pointed out by W. Davies and the present 

 writer. The skulls recorded below have a hyostylic appearance ; 

 but the writer is indebted to Dr. R. H. Traquair for the information 

 that the Edinburgh Museum acquired a specimen some years ago 

 proving the arrangement to be truly autostylic, while a pair of 

 vomerine teeth occurs in advance of the well-known lar^e dental 



