364 MB. E. S. COBBOLD ON THE [vol. lxxvi, 



granular surface ; it is larger, and tapers more rapidly than 

 H. cancellata. 



Locality and horizons. — Comley, Lower Cambrian; from 

 the Olenellus Limestone, horizon Ac„, the Microdiscus-belli- 

 marginatus Limestone, horizon Ac 3 , the JProtolenns Limestone, 

 horizon Ac 5 , and the Lapworthella Limestone, horizon Ad. 



VII. The Comley Gasteropoda. 

 Scenella Billings. 



SoENELLA ELEVATA, Sp. IIOV. (PI. XXIV, fig. 36.) 



Type and only specimen [PR 1211, Geological Survey, Rhodes 

 collection, 1892]. 



Diagnosi s. — Shell patellif orm with apex towards the anterior (? ) 

 end, depressed slightly below the highest point ; aperture not seen, 

 probably an ellipse ; posterior and lateral slopes very slightly 

 convex and inclined, anterior slope approaching the vertical ; shell- 

 substance calcareous, exterior with closely-set, impressed radiating 

 lines, scarcely visible on the upper half of the shell, but strong 

 towards the margins with the interspaces rounded ; these are 

 crossed by delicate concentric lines of growth and six or seven 

 stronger lines, which near the apex tend to form constrictions, but 

 in the remainder of the shell mark angular changes of curvature. 



Dimensions. — Length = about 3 "5 mm. ; width =3 mm.; height 

 = l - 66 mm. 



The species is referred to Billings's genus, on account of the 

 absence of pronounced concentric rugosities, though in the depres- 

 sion of the apex it resembles Held on ell a. It may be contrasted 

 with Dr. Kiser's two species, Scenella antiqua and Sc. depressa, 1 

 from Tomten. 



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

 Olenellus Limestone, horizon Ac 2 . 



Helcio^ella Grabau & Shimer. 

 Helcionella cingutata, sp. nov. (PL XXIV, fig. 37.) 



Tjrpe-specimen [827]. 



Diagnosis. — Shell patellif orm, with elevated apex; aperture 

 not known, but, as indicated by the cross-section, an elongated 

 ellipse with axes in the ratio of 5 to 2 ; apex slightly curved over 

 towards the anterior (?) end ; shell-substance calcareous, with 

 black, phosphatic, outer pellicle ; exterior marked by concentric 

 rounded fillets, set at even distances apart and separated by flat 

 or slightly concave spaces about three times as wide as the fillets 

 themselves. 



Dimensions. — The only known specimen is fragmentaiy ; it is 

 2 mm. in height and 4 in length. 



1 1916, pp. 17, 18 & pi. ii, figs. 1, 1 a-1 c, 2 a-2c. 



