496 DR WHEELTON HIND ON 



Dimensions. — Fig. 4, PI. III., a left valve, measures : antero-posteriorly, 25 mm. ; 

 dorso-ventrally, 18 mm. 



Locality. — Lower Llandovery of Mulloch Hill. 



Observations. — Only one specimen of this shell is in the collection ; but it is a well- 

 marked form, and unlike any described species to which I have had access. A reference 

 to 0. notabilis from the Middle Cincinnati group, Ohio (Ulrich, op. supra cit., pi. xlix. 

 fig. 16), will show that the Scotch shell has similar generic characters. 



Genus Pteronites, M'Coy, pars, 1884. 



Pteronites, pars, M'Coy, 1844, Synopsis Garb. Foss. Ireland, p. 81. 

 „ Hind, 1901, Mono. Brit. Garb. Lamell, vol. ii. p. 5. 



Generic Characters. — "Shell compressed, oblique, subtriangularly transverse, very 

 inequilateral ; anterior end small, sharp, and pointed. Inferior border convex and 

 posterior border sinuous. Hinge line forms the most transverse diameter of the valve ; 

 umbones small, placed anteriorly, not terminal. Valves obliquely swollen from the 

 umbo towards the postero- inferior angle. Posterior slope compressed, expanded, and 

 subalate. External surface ornamented with concentric lines and folds, more apparent 

 posteriorly and over the swollen part of the valve." 



Remarks. — I consider that the Pterinea retrojiexa, Dalm., figured in the Sil. 

 Syst., pi. v. fig. 9, should be referred more correctly to Pteronites. Another species is 

 represented in the Middle Llandovery of Woodland Point which I consider to be new. 



Pteronites ellipticus, sp. nov. (PI. I., fig. 9.) 



Specific Characters. — Shell below medium size, almost elliptical, generally com- 

 pressed, with a hollow dorsal slope. The anterior end well developed, narrow ; the 

 antero-superior angle acute. The anterior margin descends rapidly and is gently 

 convex. Lower margin strongly convex ; the posterior somewhat narrowed, truncate, 

 almost straight. 



The umbones are small, compressed, and elongate, placed about quarter of the 

 length of the hinge line from the anterior end. Proceeding from the umbo towards 

 the posterior border is a small oblique ridge which separates the compressed dorsal 

 slope from the rest of the valve. The narrow anterior end is also separated from 

 the convex portion of the valve by a broad shallow sinus. 



Interior.— The hinge plate is linear posteriorly. 



Exterior. — The surface is almost smooth. The striae of growth are somewhat 

 irregular at the anterior end. 



Dimensions. — Fig. 9, PI. L, measures : antero-posteriorly, 23 mm. ; dorso-ventrally, 

 13 mm. 



Locality. — Middle Llandovery of Woodland Point. 



