LEBESCONTIA /ENIGMATICA. 



199 



SOME ALLIES OF DITHYROCARIS. 



I. Lebescontia ^nigmatica, gen. et sp. nov. Woodcuts, Figs. 11 — 13. 



This was referred to in the " Seventh Report on Palasozoic Phyllopoda,'' 

 ' Report British Association for 1889 ' (1890), page 65, as having been collected 

 by M. Paul Lebesconte, of Rennes, from the Lower Silurian rocks of Brittany and 

 neighbourhood, thus: — " M. Lebesconte's Collection, above mentioned, comprises 

 two specimens of Dithyrocaris, one from Coesmes (Ille-et-Vilaine) and one from 

 Reuaze (Mayenne), both in the ' Schiste ardoisier superieur (Faune 2de, Barrande),' 

 above the Gres de May." 



These are specimens in rather hard, dark-blue, slaty, argillaceous schist, 

 slightly micaceous. One of them (from Coesmes) shows a hollow impression, 

 45 mm. long by 30 mm. wide, and nearly 2 mm. deep at one part of the 

 border — apparently the hollow mould of a flattened bivalve or shield-like form 

 allied to Dithyrocaris, Fig. 11. 



The other specimen (from Renaze), of similar slate, has a slight convexity of 



</\ ~ ' 'v> : r 



Fig. 11.— Lcbescoiilia iriiiffinnfirri, gen. et sp. nov. Two flattened valves or moieties. Lower Silurian, CoSsmes, 



Brittany. Magnified 1£ diani. . 



Figs. 12 A, B.— Lebescontia iniii/motiea. A. Dorsal aspect. Lower Silurian. Magnified 1£ diam. u. Raised 



or thickened dorsal ridge. Magnified 7 diam. Lower Silurian, Renaze, Anjou. 

 Fig. 13.— Lebescontia xnigmatiea. Crushed right valve. On the back of the same specimen of slate thai 



contains Fig. 12. Magnified \\ diam. Lower Silurian, Renaze, Anjou. 



