358 ME. E. S. COBBOLD ON THE [vol. lxxvi, 



spaced 4 to the millimetre. Aperture at right angles to the axis 

 of the shell. 



There appear to be no nearly-allied forms with which this specie- 

 may be compared. The apical portion, if found detached, would 

 be very similar to Torelella. 



Locality and horizon. — Comley, Lower Cambrian; horizon 

 Ac 2 (the Olenellus Limestone) of Comley Quarry. 



Hyolithus (Orthotheca) de geeri Holm (?). 



Hyolithus {Orthotheca) de geeri Holm, 1893, Sver. Geol. Undersokn. ser. C, 



No. 112, p. 54 & pi. i, figs. 25-27. 

 Hyolithus Cobbold, 1912, Rep. Brit. Assoc. (Portsmouth, 1911) p. 114. 

 Hyolithus (Orthotheca) de geeri Holm, Cobbold, 1919, Geol. Mag. p. 150 & 



pi. iv, figs. 1-6. 



Some of the casts mentioned in the British Association Report 

 agree in cross-section and apical angle with Holm's species, but are 

 not sufficiently well preserved for accurate determination. The}' 

 are smaller than the type from Scandinavia. 



Locality and horizon. — Comley, Lower Cambrian; from 

 beds which are mapped as belonging to horizon Ab„. 



Hyolithus (Orthotheca) sp. indet. a. (PL XXIV, fig. 34.) 



An oval operculum, which appears to belong to the sub-genus 

 Orthotheca, cannot be assigned to any associated shell. It is 

 almost flat, the nucleus rising a very little above the plane of the 

 margin ; the exterior is marked by numerous concentric strise and 

 two lines on each side radiating from the nucleus (which is sub- 

 central) towards the lateral much rounded angles. 



Dimensions. — Dorsi- ventral diameter = about 3 mm.; trans- 

 verse diameter = about 6 mm. 



This operculum recalls that assigned by me with reserve to 

 H. (0.) de geeri Holm, from the Hyolithus Limestone of Harts- 

 hill, Nuneaton. 1 The principal difference is that the angle at the 

 apex of the dorsal portion of the Comlev specimen is about 130° 

 instead of 90°. 



Hyolithus (Orthotheca ?) sp. indet. b. (PI. XXIV, fig. 35.) 



A very different operculum from the same horizon as the last is 

 referred somewhat doubtfully to the sub-genus Orthotheca. It 

 is sub-triangular, has the nucleus situated near the ventral angle 

 and the conical dorsal projection is very narrow, the angle at the 

 apex being only about 45°. On each side of its boundary-lines 

 two projections on the interior appear to indicate muscle attach- 

 ments. The exterior has faint stria; of growth near the margin. 

 The margin appears to be in one plane, and the plate when in place 

 would be (on the whole) concave. 



Locality and horizon for both opercula. — Comley, Lower 

 Cambrian; from the Protolenus Limestone, horizon Ac.. 



1 Cobbold, 1919, p. 150 & pi. iv, figs. 7-9. 



