506 DR WHEELTON HIND ON 



Modiolopsis minor, sp. nov. (PI. II., figs. 22, 23.) 



Specific Characters. — Shell small, oblique, triangularly ovate, moderately and 

 obliquely gibbose. The anterior end is narrow and short, its border almost elliptical. 

 The inferior margin descends downwards and backwards and is almost straight. The 

 posterior border is almost straight, obliquely truncate. The hinge line is straight, of 

 moderate length, making a well-marked obtuse angle with the posterior border. The 

 umbones are small, elongate, and twisted forwards, placed far forwards. 



Interior. — Apparently normal. 



Exterior. — The surface is ornamented with regular, close, fine concentric lines. 



Dimensions.— Fig. 23, PL II., a left valve, measures: antero-posteriorly, 13 mm. ; 

 dorso-ventrally, 7 mm. 



Locality. — Penkhill, Upper Llandovery. 



Observations. — A small species typical of the genus and possessing the characteristic 

 ornament. 



Genus Mytilops, Hall, 1884. 



Mytilops, Hall, 1884, Geol. Surv. New York, Pal., vol. v., pt. i., Lamell., i., p. xiv. 

 Miller, 1889, N. Amer. Geol. and Pal, p. 494. 



Generic Characters. — Modioliform. Hinge line straight, umbones blunt, terminal. 



Observations. — Hall established this genus for certain shells as a sub-genus of 

 Modiola. Little or nothing was known of the interior, for in neither of the two species, 

 to include which the genus was erected, were any details of the hinge plate observed. 

 In one of the shells which I now refer to this genus, the posterior part of the hinge 

 plate shows short, narrow, sub-parallel teeth, which occur in Grammatodon, Mytilarca, 

 Plethomytilus, and other palaeozoic genera. This character is enough to separate the 

 shells from Modiola. 



Mytilops subovalis, sp. nov. (PI. II., figs. 24, 25.) 



Specific Characters. — Shell below medium size, triangularly ovate, oblique, 

 moderately swollen, modioliform, compressed at the postero-superior angle and subalate. 

 The anterior end is obsolete. The anterior border, oblique and almost straight. The 

 inferior border well rounded ; the posterior oblique and straight, almost parallel with 

 the anterior. Hinge line straight, postero-superior angle obtuse. The umbones are 

 inconspicuous, merged in the obtusely pointed anterior end. 



Interior. — The hinge line has short lateral teeth posteriorly. 



Exterior. — The surface is ornamented with fine concentric lines of growth, with 

 here and there deeper concentric lines of grooves. 



Dimensions. — Fig. 24, PI. II., measures : antero-posteriorly, 25 mm. ; dorso-ventrally. 

 15 mm. 



Locality. — Middle Llandovery of Woodland Point. 



