536 DR WHEELTON HIND ON 



Localities. — Penkhill, Upper Llandovery ; Mulloch Hill, Lower Llandovery. 



Observations. — There are three specimens in the collection which I refer to this 

 genus provisionally. They resemble the figure of the type very closely as to general 

 contour and size. Unfortunately, no details of the interior are exposed. 



Genus Orthonota, Conrad. 



Orthonota, Conrad, 1841, Geol. Surv. New York, Pal. Dept. Ann. Rep., p. 50. 

 Orthonotus, pars, M'Coy, 1855, Brit. Pal. Foss., p. 274. 



Orthonota, Hall, 1885, Geol. Surv. New York, Pal., vol. v., pt. ii., Lamell., ii., p. xlv. 

 Miller, 1889, N. Amer. Geol. and Pal, p. 497. 



Generic Description. — " Equivalved, profoundly elongated. Hinge and basal 

 margins straight and parallel. Beaks near the anterior extremity ; posterior extremity 

 truncated." 



Observations. — The above is Conrad's original description, quoted by Hall 

 (op. supra cit.). Unfortunately, the hinge characters are still unknown, and little is 

 known of the interior. The type is Orthonota undulata. 



M'Coy has included in the genus Goniophora cymbwformis, which has very 

 different characters, the strongly keeled shell differing very strongly from the typical 

 forms of Orthonota. 



The true generic affinity of the genus cannot be discussed until details of the hinge 

 plate are to hand ; but it seems to me to have a close relationship with some forms 

 of Sanguinolites, e.g. S. plicatus. The genus is represented in the Devonian rocks of 

 North America by more than a dozen species. 



Orthonota inornata, Phillips, 1848. (PI. V., fig. 21.) 

 Orthonota inornata, Phillips, 1848, Mem. Geol. Surv. Great Britain, vol. ii., pt. i, p. 362, pi. xix. fig. 3. 



Specific Characters. — Shell transverse, narrow, very inequivalve. Dorsal and 

 ventral margins subparallel. Anterior end narrow, produced, its margin rounded, 

 forming an angle with the hinge line. The posterior end expanded and compressed, its 

 border truncate and oblique, making an obtuse angle with the hinge line. The umbones 

 are small, elongate, ridged, slightly raised, and situated in the anterior third of the shell. 



Proceeding from the umbo to the margin just in front of the rounded postero- 

 inferior angle, is a well-marked angular ridge, which gradually becomes obsolete as it 

 crosses the valve. The dorsal slope is hollow, and the anterior narrowed by a broad 

 sulcus. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with numerous very fine, close, concentric 

 lines, which run parallel with the margins. 



Dimen sions. -Fig. 21, PI. V., a right valve, measures: antero-posteriorly, 36 mm. ; 

 dorao-ventrally, 14 mm. 



