38 THE BRITISH CONULARLE. 



rather Less than twice the shorter (about 5:;]), but at the apex the shell almost 

 invariably appears more flattened, and the cross-section takes the form of an 

 ellipse with the longer diameter more than twice the shorter. The apical angles of 

 the faces vary in different specimens, but the measurements are not always trust- 

 worthy, and the greater number give values between 10° — 12°. 



The apertural lobes are not usually seen, though there are several specimens 

 known which show them in a more or less nearly complete state. They are short, 

 with gently rounded apices, and bend down at right angles to the axis of the shell 

 (PL V, fig. 8). In almost all cases the shell is closed at the apical end by a gently 

 convex septum (PL V, figs. 7 b and 9), and rarely, if ever, does it taper to a 

 sharp point. The septum occurs at varying distances from the aperture, and this 

 fact points to the probability of the existence of more than one such partition in 

 the length of the shell. Indeed, in one specimen, from the Museum of Birming- 

 ham University, G mm. above the terminal septum the shell is broken away, and 

 another and quite similar septum is seen, passing inwards parallel to the other, 

 and apparently continuous with the thin inner layer of the shell. The ornamenta- 

 tion is of the typical cancellate type. The point of angulation of the transverse 

 folds is perceptibly nearer to the "central" than to the "lateral" marginal grooves, 

 and the ridges meeting in the " central " groove from adjacent faces form an angle 

 approaching 180°. In the apical half of the shell the ridges form straight-sided 

 chevrons across the face, but towards the aperture there is a marked increase in 

 the size of the angle, and the straight lines are replaced by broad, compound 

 curves, at first concave, then convex to the aperture as they pass down from the 

 point of angulation to the marginal groove. 



The tubercles on the ridges are sometimes well preserved, but more often are 

 reduced by friction to small rounded hollows ; still more frequently the ridges arc 

 worn down to coarse, rough projections, and in the furrows between these the shell 

 is well preserved, and the close and regular vertical striation is clearly seen. If 

 the outer layer of the shell is removed, the thin yellowish under-layer is exposed, 

 ornamented in the same way as the outer, but much less strongly (PL V, 

 fig. 10 fc). 



Affinities. — This shell is the commonest British representative of a type that is 

 widely spread all over the globe. It is very similar to the Bohemian species, 

 G. proteica, Barrande, and to the Swedish G. cancellata, Lindstroni, but it is 

 doubtful whether it is identical with either of these. Species with strongly can- 

 cellated ornamentation appear to have flourished in highest Ordovician and Silurian 

 times, and during this period gave rise to local types (G. planiseptata, vesicularis, 

 breviconventa), which cannot be identified with species of other countries. 

 Lindstrom's species, C. cancellata, ranging from the Brachiopodskiffer to the 

 highest Silurian of Gotland, may possibly in the same way include more than one 

 local species, but 1 was not able to identify any with the British forms. 



