LEBESCONTIA ^MGMATICA. 



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 Dithi/rocaris, one from Coesmes (Ille-et-Vilaine) and one from 

 Renaze (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 neai'ly 2 mm. deep at one part of the 

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

 allied to BitJujrocaris, Fig. 11. 



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



Fjg. 11. 



Fig. 12 a. 



Fig. 12 B. 



Fig. 13. 



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Fig. \l.~Lebescontia lenigmatica, geu. et sp. nov. Two flattened valves or moieties. Lower Silurian, Coesmes, 

 Brittany. Magnified \\ diani. -o • a 



Figs. 12 a, ^.—Lebescontia xniymaiica. A. Dorsal aspect. Lower Silurian. Magnified 1| diam. B. Kaised 

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



Fig. \i.—Lehescontia lenigmatica. Crushed right valve. On the backof the same specimen of slate that 

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



