lxxii INFERIOR OOLITE AMMONITES. 



6. Ludwjgia ambigua (>S Y . Buclcman). Plate VII, figs. 1, 2 ; Suppl., Plate XVII, 



figs. 31 a, b. 

 188S. Lioceeas ambiguum, This Monogr., PI. vii, figs. 1, 2. 



Description. — Platyleptogyral, excentrumbilicate ; parvicostate declining to 

 striate. 



Distinction. — From L. Isevigata, the mode of coiling the umbilicus. There is 

 also a difference in the curve of the radial line. 



Remarks. — The placing of this species in the genus Ludwigia, which is another 

 way of expressing its direct genetic affinity with L. Murchisonse, may not be justifi- 

 able, and the genetic affinity may be doubted. Of the two curves of the radial 

 line given, the first or earlier one (fig. 31 a) requires consideration ; it should 

 agree with that of L. Murchisonse. It has a certain resemblance. The later radial 

 curve is interesting for its hypostrophic character — the loss of peripheral projection. 

 It is associated with the striate stage, the umbilical expansion, and the decline of 

 the carina, which are also hypostrophic characters. 



Locality and Stratum. — Dorset : Bradford Abbas, in the Paving Bed or its 

 associated marl. Foreign : Normandy (Calvados), " Feuguerolles, Murchisonse 

 [beds], upper part " (from Dr. L. Brasil, two specimens). 



Date of Existence. — Bradfordensis hemera, in all probability. 



XXV. Genus — Rh^iboceras, 1 S. Buclcman. 



(Type — Rhsehoceras tortum, sp. n.) 

 1899. KHiEBOCERAs, This Monogr., Expl. of Suppl. PI. XI. 



Definition. — Platysubpachygyral, sublaturabilicate ; laterally 

 anguliradiate ; peripherally anguliradiate, subfastigate, parvi- 

 nonsepti-carinate. 



Fig. 28.— Radial _..,. ,. T1 T 7 . . 



Hue of Distinction. — From Ludwigia, more compression in proportion 



tortwmT to umbilication, and the radial line not quite so bent laterally. 



1. Rh^boueras tortum, 8. Buclcman. Suppl., Plate XI, figs. 1 — 3. 



1874. Ammonites Muhchison-e, Dumortier, Etudes pai. Bassiu Ehone, pt, 4, 



pi. li, tigs. 5, 6 (non 3, 4). 

 1874. — tolutaeius, Dumortier, in Coll., p. 256. 



Description. — Platysubpachygyral, sublatumbilicate, costate. 

 Locality and Stratum. — Burton Bradstock, in the greyish-blue limestone above 

 the sands, the Lioceras uncinatum bed. 

 Date of l<lr isle nee. — Scissi hemera. 



1 Yaijios, crooked, beut. 



