126 Dr. L. Hussakof — U. Devonian Arthrodira from Ohio. 



to those figured by Dean ' in the type of S. Kepleri, except for defects 

 in preservation, having lost their anterior extremities and the minute 

 denticles. They differ considerably in form from the mandible figured 

 in inner and outer aspect by Claypole in his original description, but- 

 it is impossible to say to what extent his figure is a restoration. His 

 figures of this species are not very accurate, missing parts being 

 restored with too much certainty and in most cases not being indicated 

 by dotted lines. The cranium is drawn from disarticulated plates 

 as if it were a complete specimen, and is altogether too pointed and 

 drawn out in front. The anterior dorso-lateral is also partly restored, 

 the posterior part being, as he says, " somewhat restored and may not 

 be quite true to nature." 



In the specimen in the British Museum (PL VIII, Fig. 4) the 

 median occipital plate displays the inner aspect and closely resembles 

 the corresponding element in S. Kepleri? The clavicular, which was 

 described by Claypole as a suborbital, is also preserved. It agrees 

 exactly with the one figured by Dean. 3 



From these facts it appears that T. Irevis, Claypole, is identical 

 with S. Kepleri, Dean. The amended name of the species is S. Irevis 

 (Claypole). 



4. Stenognathus Gouldi (Newberry). (PI. VIII, Fig. 5, and 

 Text-figure, Fig. 6.) 



1885. Dinichtliys Gouldii, Newberry, Trans. N.Y. Acad. Sci., p. 26. 



1889. D. Gouldii, Newberry, Paleoz. Fishes, p. 150, pi. ix. 



1889. D. corrugatus, Newberry, ibid., p. 151, pi. vii, figs. 3, 3a. 



1893. D. gracilis, Claypole, Amer. Geologist, vol. xii, p. 279, fig. 



1896. D. Gouldi, Newberry (ed. Dean), Trans. N.Y. Acad. Sci., vol. xv, p. 157, 



pi. vii. 



1897. Stenognathus corrugatus, Newberry (ed. Dean), ibid., vol. xvi, p. 30, 



pl. xxiv, figs. 27, 28. 



1908. Dinichtliys Gouldi, Newberry, Hussakof, Bull. Amer. Mus. Nat. Hist., 



vol. xxv, p. 8, fig. 1. 



1909. Stenognathus corrugatus, Hussakof, ibid., vol. xxvi, p. 267, fig. 4. 



The writer has recently shown (1909) that the mandibles described 

 under the names S. corrugatus by Newberry and D. gracilis by Claypole 

 are the same, and that the genus Stenognathus should stand as distinct 

 from Dinichthys. In the British Museum there is a specimen (P. 9335) 

 which shows a pair of similar mandibles, and associated with them 

 a number of disarticulated elements of the same individual, including 

 the cranium, suborbital, maxillary, premaxillary, and several dorsal 

 and ventral armour plates. This specimen is, therefore, of especial 

 interest since it acquaints us for the first time with the head and body 

 armour of the form known as Stenognathus. Furthermore, there are 

 two elements in this specimen, the premaxillary and the suborbital, 

 which are of quite distinctive form and may be told at a glance from 

 the same elements in other Dinichthyids ; and by reason of this very 

 distinctiveness of form these elements are seen to agree closely with 

 the corresponding ones in the specimen which was described by 

 Newberry as D. Gouldi. The mandibles of the latter were represented 



1 Mem. N.Y. Acad. Sci., vol. ii, pl. vi, fig. 36. 



2 Ibid., pl. vi, fig. 33, MO. s Ibid., fig. 38. 



