184 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



equal parts by a sharp, elevated keel ; tlie anterior side wrinkled with 

 coarse irregular folds, which are crossed near the lip in old shells by- 

 longitudinal wrinkles ; posterior side nearly smooth with irregular 

 lines of growth. Smaller valve incurved and entirely smooth. 



Length 2 to 3 inches. 



Abundant in the upper beds of the hippurite limestone at Lisbon, 

 and in the subcretaceous limestone of the cliff of the Praia de Ma9ams 

 near Cintra. 



This curious shell is readily distinguished by the sharp ridge along 

 the larger valve. It resembles the D. Lucii (as seen in M. Fa\Te's 

 figures, * Observations sur les Diceras,' pi. 1. fig. 2. &c.), both in the 

 wrinkling of the anterior side of the larger valve and in the contrast 

 which that presents to the smoothness of the smaller valve. My 

 specimens do not show the hinge completely ; the casts of both valves 

 bear the deep impression of a strong plate proceeding from the umbo 

 nearly to the edge of the valve (see fig. 3 c), as is shown in the figure 

 of D. Lonsdalii (Geol. Trans. 2nd series, vol. iv. pi. 13. fig. 4), and in 

 M. Favi^e's fig. 5, 6 & 7 of plate 5, where it is marked m. This 

 plate appears to bound the muscle, as in Cucullcea, &c., and is no way 

 connected with the hinge, as might be inferred from M. Favre's de- 

 scription (p. 15, and pi. 5. fig. 1), where I presume that the artist has 

 misrepresented the plate m in question. 



The Portuguese specimens show the different layers of shell de- 

 scribed by M. Favre, after whom I have much pleasure in naming 

 the above species, in gratitude for his valuable additions to our know- 

 ledge of this curious genus. 



Plate XV. fig. 3 « & 6. Two views of the same specimen, from 

 the hippurite limestone. 



Fig. 3 c. Cast of the interior of another specimen, from ditto. 



Plate XX. fig. 9. Small specimen from the subcretaceous beds 

 of the Praia de Ma9ams. 



ExoGYRA FLIC AT A, Lamarck, sp. 



E. plicata, Goldfuss, pi. 87. f. 5. 



E.Jlabellata, Goldfuss, pi. 87. f. 6. 



OstrcBa Boussingaultii, D'Orb. T. Cret. pi. 468. 



O.Jlabellata, D'Orb. T. Cret. pi. 475. 



O. Matheronia7ia, D'Orb. T. Cret. p. 485. 



GryphcBa harpa, Forbes, Journ. of Geol. Soc. vol. i. pi. 3. f. 12. 



Few species have been more subdivided than the Gryphcea plicata 

 of Lamarck, partly owing to the variations of its form and partly to 

 the determination of the author who has laboured most efficiently in 

 this field to find a distinct species in each subdivision of the creta- 

 ceous system, until by a strange fatality the original specific name 

 seems in danger of dropping through entirely. 



The specimens which I have brought from Portugal are principally 

 derived from two localities, belonging to two very distinct parts of the 

 cretaceous system : the hippurite limestone or upper bed representing 

 the chalk, well exposed at the quarries in the valley of Alcantara close 



