CYTHEREIS LONSDALEANA. 27 



G. Icenica is named after the Iceni — the old inhabitants of Norfolk, whence 

 alone as yet the type form of this species has been obtained. 

 Locality. — Chalk, Thorpe, near Norwich. 



7*. Cytherbis Igbnica, sp. nov., var. quadrata, nov. (vel Icenica-quadrata). Plate 



I, fig. 62; and Plate IV, figs. 15—17. 



PI. I, fig. 62. Length '47 ; height "27 mm. 

 • PI. IV, fig. 15 ,, '53 ; „ "33 ; thickness '3 mm. 



Among the specimens collected from the siliceous meal in a Horstead flint are 

 several specimens (some very small) referable to G. Icenica, but varying in 

 breadth (height), and in the curvature of the dorsal and ventral margins. Some 

 are subquadrate, rounded in front and angular behind, retain traces of a coarse 

 punctation, and have the middle and marginal elevations much modified. PI. I, 

 fig. 62, and PI. IV, fig. 15, show individuals having a strong, straight ventral 

 ridge, ending with an angle. Another (not figured), instead of the low central 

 and ventral elevations, has two parallel, thin, sharp ridges. These somewhat 

 square forms may be grouped as variety quadeata. 



Locality. — Chalk, Horstead, Norfolk. 



8. Cythereis Lonsdaleana, Jo7ies. Plate I, figs. 40 — 42, 64 — 66. 



Cytheeeis Lonsdaleiana, Jones. Monogr. Entom. Cret., IS^iO, p. 20, pi. v, 



figs. 12 a — c. 



height '35 ; thickness '25 mm. 

 ,, '38 mm. 

 J) *38 „ 

 thickness "38 mm. 



These suboblong, or obovate, valves are not very common. Individuals differ in 

 details as to proportionate height of valve, and the thickness and extent of ridges, 

 but the species is characteristically distinct. Thus figs. 40 — 42 are more oblong, 

 and have the ridges thinner and less pronounced than in the individuals first 

 figured, one of which (right valve, fig. 12 h) is much more obovate than the other 

 (left valve, fig. 12 a). 



Localities. — Chalk, Norwich and Horstead ; Chalk-rock, Dunstable. A similar 

 form occurs in the Upper Oolite (soft white limestone with flints), at Ridgway, 

 Dorset. 



Fig. 40. 



Length "67 



Fig. 64. 



„ -72 



Fig. 65. 



„ -61 



Fig. 66„ 



„ -83 



