part 4] CAMBRIAN HORIZONS OF COMLET. 365 



Observations. — Similar concentric fillets are shown in Shaler 

 & Foerste's figure l of their species Stenotheca curvirostra, which 

 is different in general form and has longitudinal stria?. 



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

 Protolenus Limestone, horizon Ac,. 



Heliconella oblonga, sp. nov. (PI. XXIV, figs. 38 & 39.) 



Stenotheca Cobbold, 1911, Q. J. G. S. vol. lxvii, p. 297. 



Type-specimen [1316]. 



Diagnosis. — Shell patelliform, with apex strongly recurved; 

 aperture oblong, with straight parallel sides and rounded ends ; 

 apex moderately sharp, bent down over the anterior (?) end to a 

 height of about '75 of the maximum, and at a point a little short 

 of the anterior border ; shell-substance thick and calcareous ; 

 exterior marked \>j very regular, step-like, concentric corruga- 

 tions, retaining throughout the form of the aperture, also by 

 numerous radiating thread-like raised lines spaced about five to the 

 millimetre and increasing by interpolation ; interior smooth, 

 except for the reproduction of the external corrugations. 



Dimensions of t} r pe-specimen. — Length = 14 mm. ; width = 

 9 - 5 mm. ; greatest height=4 mm. ; height of apex=about 3 mm. 



Observations. — This species occurs fairly plentifully in the 

 matrix of the Middle Cambrian conglomerate of Comley Quarry, 

 and is readily identified, even when poorly exposed, by the regu- 

 larity of sculpture and the form of aperture. These features also 

 serve to separate it from H. rugosa (Hall) and from other Comley 

 forms of the genus. 



The regularity of the step-like corrugations recall those shown 

 in J. W. Salter's figure' 3 of Stenotheca cornucopia from the Middle 

 Cambrian of South Wales. That species is preserved in shale, and 

 appears to have had a thin shell. 



Locality and horizon. — Comley, Middle Cambrian, horizon 

 Ba t ; from the Conglomerate of Comley Quarry, and from the same 

 bed at Kobin's Tump. 



Helcionella rugosa Hall, var. comleyensis nov. (PI. XXIV, 

 fig. 40.) 



Metoptoma rugosa Hall, 1847, Pal. N. York, vol. i, p. 306 & pi. lxxxiii, figs. 6«-6c. 

 Stenotheca rugosa Hall, Billings, 1872, Canad. Nat. n. ser. vol. iii, p. 479. 

 Stenotheca rugosa Hall, Walcott, 1886, Bull. U.S. Geol. Surv. 30, p. 128 & pi. xii, 



figs. 1, 1 a-\ e. 

 Stenotheca rugosa, Hall, Walcott, 1890, lOtli Ami. Rep. U.S. Geol. Surv. p. 617 



& pi. lxxiv, figs. 1, 1 a-\ e. 



Type for variety [1897]. 



This variety differs from the more typical forms of the species 

 in the character of the encircling rugosities. The aperture is a 

 wide ellipse, ratio of axes 1 to - 9 ; the concentric rugosities of 



1 Bull. Mus. Comp. Zool. Harvard, vol. xvi, No. 3, p. 30 & pi. i, fig. 8. 



2 1872, Q. J. G. S. vol. xxviii, p. 180 & pi. vii, figs. 12-13. 



