GYROPLEURA. 209 



of the type) and with d'Orbigny's figs. 4 and 5. The ornamentation in this 

 species is imperfectly known ; most of the examples from Ronen are either 

 internal casts or have only portions of the shell present, on which the orna- 

 mentation is rather indistinct. In one specimen from Dorset part of the shell 

 of the fixed valve is preserved ; the radial ribs are not so prominent as in 

 Ct. ivpijiiiroKh-iifd, ])ut concentric lamellte are distinct. 



Distribiifinn. — Chloritic Marl of Melbury Park and Chaldon, Dorset. Recorded 

 by Jnkes-Browne from the base of the Lower Chalk of C'liard and Maiden 

 Newton. 



GYRorLEURA INEQUIROSTRATA {Wondivard), 1 880. Plate XXXIII, figs. 8 — 13. 



1833. DiCERAS iNEQUiRosTRATus, S. Wondivard. Geol. Norfolk, p. 47, pi. v, fig. 22. 

 1854. Chama in.«quirostrata, J. Morris. Cat. Brit. Foss., ed. 2, p. 194. 



Description. — Shell nmch inflated. Right valve large, oval, attached by a 

 considerable portion of the anterior side; nmho prominent, pointed, incurved 

 anteriorly. Left valve capuliform, with the umbo near the hinge-margin. 



Ornamentation consists of strong, lamellar radial ribs, which are undulose 

 where they cross growth-i'ings. The ribs have strongly serrate summits and 

 are separated by rather broad, flat, smooth interspaces ; sometimes the serrations 

 are replaced by iininerons transverse, scale-like structures. Near the fixed part 

 of the ri<j;ht valve the ribs are more numerous than on the flank. 



Measirremeids of fixed value. : 



(1) (2) 



Length . . 22 . ID 



Height . .28 . 2(5 



(1 — 4) Norwich. 

 AJfinifie!<. — G. rijili/aiia (dc Ryckholt),' from Ciply, differs from this species 

 in having the ribs more widely separated and in the presence of small ribs in 

 the inter.spaces and on the sides of the main ribs. CI. rn.'isiensi.v (d'Orbigny)- 

 i-eseml)les closely G. ineqnirostrata and was regarded by Morris as a synonym of 

 the hittei-, but it possesses small ribs on the sides of the main ribs.^ 



1 ' Mi'laii-es Tak-uut.," pt. ii (18.51), p. 179, pi. xii, %s. 12, 13; Douvilk', 'Bull. Soc. gc'ol. de 

 Fniuce,' ser. 3, vol. xv (1887), p. 744, pi. xxviii, fig. 11 ; Holzapfel, ' Mollusk. Aachen. Kreide ' (1889), 

 p. 189, pi. xix, figs. 5, 6; Wollemanu, ' Fauua d. Liiuelmrg. Kreide' (1902), p. 75, pi. ii, figs. 5, 6. 



- Murehisou, de Vernciiil, and de Keyserliug, ' Gcol. do la Kussie,' vol. ii (1845), p. 49(j, pi. xliii, 

 figs. 31—33 ; Douvilk', 'Bull. Soc. gc'ol. de France,' ser. iii, vol. xv (1887), p. 775, pi. xxviii, fig. 13. 



» G. Miinsteri (v. Hagenow) is probably related to O. hmqmrontrala. See Kavii, ' MoUuslc. i 

 Daniuarlis Kr.-idtafl. I. Laiiullibr.' (1902). p. 12(5, pi. iv, figs. 10, 11. 



