46 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
Shell small, inflated, short, subtrigonal ; umbones depressed, mesial, obtuse and incurved; 
the anterior border is rounded, sloping downwards and uniting with elliptical curvature of 
the lower border ; the posterior side slopes abruptly downwards, it has an oblique posterior 
carina, which becomes conspicuous and raised towards its lower extremity ; it separates a 
posterior, depressed, lanceolate area from the sides of the shell. ‘The surface has obscure 
longitudinal striations, and several folds of growth. 
The inflated figure, short posterior side and projecting oblique posterior carina, dis- 
tinguish it from Leda /achryma, Sow., and also from other species of the Lower Oolites. 
Geological Positions and Localities. 'The Cornbrash of Scarborough, in which it occurs 
rarely, Professor Phillips records it in the lower stage of the Inferior Oolite (Dogger), 
and in the gray limestone or upper stage of the same formation upon the coast of Yorkshire. 
Triconta ELONGATA, Sow. Tab. XXXIX, figs. 6, 6 a. 
TRIGONIA ELONGATA, Sow. Min. Con., t. 431. 
— — D Orb. Prodr., vol. i, p. 338. 
ns — Morris. Catal., 1854, p. 228. 
— — Oppel. Juraformation, p. 525. 
— — Damon. Geol. Weymouth, Suppl., pl. 2, figs. 1, 2. 
Testa subtrigona, alta, convexa, antici brevissima truncata, costis, magnis, subhorizon- 
lalibus, leviter undulatis ; umbonibus prominentibus acutis incurvis; area cardinali lata, 
ornatissima, distincte tripartita, carinis prominentibus, denticulatis. 
Shell subtrigonal, very convex and lengthened ; anterior side short, its border abruptly 
truncated with numerous large, nearly horizontal and slightly undulated cost; the 
umbones are elevated and much incurved ; the posterior area (which nearly equals in size 
the other portion of the surface) is very wide, and is separated into three distinct parts by 
as many prominent denticulated carine; the marginal carina is very large and nearly 
straight ; the mesial and inner carinze though smaller are likewise conspicuous in both the 
valves ; the space between the mesial and inner carima is much depressed and its orna- 
mentation is very delicate ; the superior or post ligamental space is short and wide, it has a 
few elevated perpendicular plications. The convexity of the united valves is somewhat 
greater than the breadth of the shell, and equal to two thirds of the length of the marginal 
carina. ; 
‘’he general figure and other characters are so strongly defined that it will not readily 
be mistaken for any other example of the group of the Costat@ ; the figure of the Cornbrash 
specimens agrees with those from the Oxford Clay, but the sculpture upon the area is less 
strongly marked in specimens from the latter formation, which are also usually smaller. 
Compared with other examples of the same group of species, Z elongata is remarkable 
for the short, widely-separated horizontal costa, for the great size and straightness of the 
