338 MR. E. S. COBBOLD OX THE [vol. lxxvi, 



greater elevation of the ventral valve, and by being slightly 

 elongate instead of decidedly transverse. 



Locality and horizon. — The Cwms sub-area of Comley, 

 Lower Cambrian ; from the Oholella-groomi Beds, horizon Ab r 



OBOLIRE King. 

 Oboltts Eichwald. 

 Obolus paetulus, sp. nov. (PL XXII, figs. 13-19.) 



Type-specimen [1512 a]. 



Diagnosis. — General form ovate, bluntly acuminate, apices 

 marginal ; dorsal valve, length and width sub-equal ; ventral valve 

 longer than wide ; convexity moderate, about a sixth of the 

 width ; shell, apparently calcareo-corneous, consisting of two 

 principal layers, weathering white or bluish white ; exterior with 

 from three to six well-defined lines of growth, numerous faint con- 

 centric striae and occasional traces of radiating lines, in the dorsal 

 valve there is an incised mesial line ; interior of ventral valve 

 showing the pedicle-groove and, continuous with it (though 

 marked off by a transverse line) the concave visceral area, on 

 each side of which are traces of the main vascular sinuses : 

 interior of dorsal valve showing a narrow but well-marked mesial 

 ridge, which near the middle of the valve gives off: outward 

 curving branches on either side, the mesial ridge widens out pos- 

 teriorly and, in the casts, is lost in the impression of the area. 



Dimensions. — Nineteen valves measured from *9 to 2"35 milli- 

 metres in length ; the average proportion of length to width in 

 ventral valves is 1 to '8, in dorsal valves 1 to *9. 



The ventral valve of O.parvulus is very like O. parvus Walcott l 

 from the Lower Cambrian of the Rocky Mountain province. 



The dorsal valve of the Comley species differs in being longer 

 than wide, and the mesial depression is much narrower than that 

 shown in Walcott' s figure. 



The surface-character of O. parvus, said to be like that of 

 Lingiolella (Lingulepis) longinervis Matthew [(?) a clerical error 

 for L. (L.) gregioa Matthew] has not been observed in O.parvulus. 



Locality and horizon. — Comley, Lower Cambrian; from the 

 Olenellus Limestone, Horizon Ac, , the JKicrodiscus-bellirnarqinatus 

 Limestone Ac.,, and the Protolenus Limestone Ac 5 . 



Obolus (?) liottarssoki, sp. nov. (PL XXII, figs. 23-2-5.) 



Obolus (?) sp. indet., Linnavsson, 1876, Bihang Iv. Svensk. Akad. Handl. vol. iii, 



No. 12, p. 16 & pi. iii, fig-. 31. 

 (?) Lmgulella sp. indet.. Matlev, 1911, Q. J.G.S. vol. lxvii, p. 301 & pi. xxvi. 



fig. 7. 

 Obolus sp. indet. g, Walcott, 1912, Monogr. U.S. Geol. Surv. vol. li, p. 423. 



Linnarsson's description is as follows: — 



' The shell is very slightly convex ; its circumference resembles a sector of 



1 1912, p. 408, text-figs. 37 a & 37 b. 



