54 MOLLUSCA FROM THE GREAT OOLITE. 



nearly internal, placed in the trigonal fossa beneath the umbones, margins of the valves 

 entire. 



The smooth valves, mesial cardinal fossa, subquadrate form, and entire margins 

 distinguish it from Pectuncuhs. The general character of the hinge presents an approxi- 

 mation to Limea, Goldfuss, both in the curvature of the series and form of the teeth ; the 

 latter genus may in fact be regarded as a representative of Limopsis amongst the Lima. 

 In Nucida the series of teeth form an angle, they are narrow and raised like a comb. 



Lnropsis ooliticus, D'Jrc/tiac, Sp. Tab. V, fig. 16, lCr/. 



Pectuxculus ooliticus, D'Archiac. Mem. Soc. Geol. Fi\, t. v, t. 27, f. 6, 1843. 

 ? — oblongus, Sow. Min. Con., t. 4/2, f. 6, 1824. 



? — minimus, Sow. Ibid., t. 472, f. 5. 



Testa laevigata oblongd, convexo-pland, subcompressd incequilateratd, umbonibus pro- 

 minulis, obliquis, lateribus oblique truncatis. 



Shell smooth, oblong, more or less transverse, convex but somewhat flattened, 

 inaequilateral, umbones prominent, oblique, the sides obliquely truncated, the lower 

 margin lengthened and curved. 



This species, which is very abundant, occurs under several varieties of aspect ; the hinge 

 line may be nearly straight and angular, or rounded ; the figure may differ much in the 

 degree of convexity, and in the length transversely; all the specimens are larger than the 

 Ancliff shells which were figured in the ' Mineral Conchology' under the specific uames 

 P. minimus and oblongus, but which, nevertheless, we are disposed to regard as only varieties 

 of the present species, and to these we might add another variety, which together with a 

 short superior or hinge border, has several irregular folds upon the surface, giving it a 

 rugose aspect. Owing to the great abundance of the species, we are at any time 

 enabled to compare these varying forms, the test being thick, always well preserved, and 

 never compressed. It occurs indifferently in all the shelly beds, and is one of the most 

 common shells of the formation. 



The Limopsis Dammariemis of Buvignier, ' Geol. dela Meuse.'p. 20, pi. 16, f. 26 — 29, 

 has some resemblance to our species, but has greater convexity and less angularity of 

 figure. 



Localities. The entire formation in the Minchiuhampton district ; Ancliff, WUtshire. 

 Eparcy, Langrune, France. 



Trigonia, Bruguiere, 1791. 



Tkigoni a, Lam., 1804. Park, 1811. Sow., 1815. D'Orbigny, 1850. 

 Hippocephaloides (Nucleus), Plot., 1676. 

 Lyriodon, Bronn, 1836. Lyrodon, Goldfuss, 1838. 



Gen. Char. Subtrigonal, rounded anteriorly, truncated posteriorly with an oblique 



