Yol. 52.] ASSOCIATED BEDS, IN N. DEVON AND W. SOMERSET. 



267 



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given by Davidson in the full description in his memoir, published 

 by the Palaeontographical Society, vol. iii. pt. vii. p. 159, can be 

 made out in our specimens : — ' Transversely oval ; hinge-line nearly 

 straight and shorter 



than the width of Fig. 3. — Impression of Stricklandinia lirata 

 the shell . . . sides from Mullacott Quarry. (Natural size.) 

 and front rounded. 

 Valves moderately 

 convex. Dorsal valve 

 more or less semi- 

 circular and trilobed, 

 from the presence of 

 a rather wide mesial 

 fold of small elevation 

 which, commencing 

 at the extremity of 

 the umbonal beak, 

 gradually widens as 

 it approaches the 

 front. Surface of 

 valves ornamented 

 with numerous angu- 

 lar, irregular, often 

 bifurcating ribs, and 

 concentric lines of 

 growth. Near the 

 umbo of the dorsal 

 valve are two elon- 

 gated pear - shaped 

 impressions, due to 

 the adductor or 

 occlusor muscles, 

 divided in the middle 

 by a central ridge. 

 Numerous pits (rough 

 tubercles on the 

 cast), probably ova- 

 rian markings, sur- 

 round these scars.' 

 The specimens are 

 so much compressed, 

 and also drawn out 

 of shape by the cleav- 

 age, that it was only 

 by the examination 

 of a large number 

 that all these points 

 could be clearly made out. There can, however, be no doubt 

 that the fossil is either S. lirata or a very closely-allied species. It 

 is an important fossil in denning the horizon, and the other fossils 



[Reproduced from a photograph.] 



