SILUKIAM OSTEACODA FROM NORTH AMERICA, ETC. 547 



IX. Leperditia, Eouault, 1851. 

 ' Ann. Mag. Nat. Hist.' November 1881, p. 334. 



15. Leperditia frontalis, sp. nov. (PI. XXI. figs. 8«, 8 6.) 



Length 6*2 mm. ; height 4-7 mm. ; thickness 3 mm. 



This is a small, subquadrate, or rather subrhomboidal, valve, with 

 the general aspect and the ocular tubercle of Leperditia ; its muscle- 

 spot is not visible ; but its ventral margin is thickened, hence pro- 

 bably it is a Leperditia and not an Lsocliilina. 



In outline and contour it would be like figs. 5 & 11, pi. i. ' Quart. 

 Journ. Geol. Soc' February 1890, were it not so oblique from above 

 downwards and backwards, and less convex. Our specimen has 

 the antero-dorsal angle well forward, the antero-ventral margin 

 sloping inwards, and the postero-ventral margin boldly curved out- 

 wards. It is somewhat like fig. 12 a (loc. cit.)^ but the front dorsal 

 angle is more pronounced, and there is no fold or sinus on the ven- 

 tral margin. So also it approaches P. Schmidt's figure of a variety 

 of Z. Hisingeri, ' Mem. Acad. Imp. Sci. St.-Petersb.' ser. vii. vol. xxi. 

 No. 2, 1873, pp. 9, 16, & 25, figs. 22, 23 ; but its front dorsal 

 angle is too prominent. An unnamed Lower-Silurian Leperditia 

 from the East of the Cordillera of San Juan, in the Argentine lle- 

 ])ublic (E. Kayser, ' Palseontographica,' Suppl. III. 1876, p. 10, pi. i. 

 fig. 19), matches E. Schmidt's variety of Z. Uisingeri. Lj. cana- 

 densis, var. anticostiaQia^ (L. anticostiensis), Jones, ' Ann. Mag. Nat. 

 Hist.' Nov. 1881, p. 344, pi. xix. fig. 8, is also near our specimen, 

 but difi'ers in the outline of its anterior moiety. On account of the 

 antero-dorsal angle being so strongly pronounced, the Leperditia 

 under notice may, I think, be called frontalis. It occurs in a 

 grey limestone made up of fragments of Encrinites, Polyzoans, Tri- 

 lobites, Brachiopods, &c., in the Division 3 of the Anticosti Group, 

 near the Jumpers, Anticosti. Coll. Dr. G. J. Hinde, E.G.S. 



I. Prtmitia, J. & H. (See also page 235.) 



16. Primitia Eillingsii, sp. nov. (PI. XXI. fig. 10.) 



Length, with fringe, 2*4 mm. ; without fringe 1*9 mm. 

 Height, „ „ 1-4 „ „ „ 1-2 „ 



This is a fine oval-oblong, or semioval (longwise), convex, smooth, 

 Primitian valve, with the umbilical pit large, round, shallow, and 

 low down (below the middle line). A nearly uniform, wide, flat, 

 thin, and delicately radiate lip is attached to the free margin, and 

 is rather narrower in front than behind. 



There is no evidence of a definitely thickened condition of the 

 margin behind the flange ; if there were, it might be grouped as 

 EurycJiilina (see p. 239). 



This form is closely allied to both Primitia plana, Krause, and 

 P. cincta, Xr., ' Zeitschr. d. D. g. Ges.' 1889, pi. i. fig. 1 & fig. 4 ; but 



* This should be anticostiensis accordinor to rule. 



