470 CEETACEOUS PELECYPODA 



straio-ht or slightly curved; the muscular impression very elongated, obtusely 

 pointed above (or anteriorly,) and marginal. 



Localities. — ComarapoUiam, Ootacoil, Arrialoor, Poodoopolliam, &c., in a 

 wliitish sandstone, or more commonly in a soft white or reddish calcareous rock. 



Forma lion. — Arrialoor group. 



This species again is one of the most characteristic fossils of the upper series 

 of cretaceous deposits, (Santonien of Coquand). It was found almost in all 

 parts of Europe, where these deposits have been traced out, as well as in North 

 America and in Northern Africa. Forbes (Trans. Geol. Soc, Lond., vii, p. 57,) 

 already indicated its occurrence in Southern India, referring to a species " allied 

 to, if not identical Avith, the Greensand Ostrea prionata.'" Many of the Indian speci- 

 mens attain a length of 200 m. m., and the greatest height of both valves some- 

 times reaches 100 m. m. 



6. OsTREA [Alectrtonia] tjngtjlata, Sehlotlieim, PL XLVII, Figs. 3 — 5. 



1813. Oitracites ungulatus, Schlotheim, Taschenbach, vii, p. 112. 



1846. Ostrea tegulanea* Forbes, Traus., Geol. Soc, Lond., vii, p. 156, pi. xviii, fig. 6. 

 1817. „ Foniiceriana, d'Orbignj', Voy. d' Astrolabe, Pal6oiit., pi. 5, figs. 45-46. 



1869. „ ungulata, Coquand, Mon. Ostrea cret., p. 58, cum synon. 



Ost. [Alectr.] sig^noidea, angiista, cequivalvi, ad umhones compressinsmla, auri- 

 cidis latemlibus irregidaribus, paido expansis seu ohsoletis, valcis area mediana 

 angiista, deplanata, Icemjata, leciter undidata, lateribus ahruptis, plicis fere ver- 

 ticaUbiis crassis et ad marginem dentatis mimitis ; atcricula latiuscula prope um- 

 hones in latere concavo sita, plicis august ioribtis acidic, modice curvatis, instructa. 



This species is characterised by the plain and smooth median space which 

 runs the whole length of the valves, the sides being abrupt, sometimes almost 

 vertical, and ornamented with single thick ribs which are along the middle 

 generally furrowed, on account of the strongly projecting teeth of the opposite 

 valve. On the convex side the ribs gradually increase in thickness from the 

 umbones, but on the concave side there is a somewhat expanded area, stretching 

 from the beaks to more than one-third the length of the sheU, covered with slightly 

 curved, thin, and sharp ribs. On the internal side of this expansion lies the mus- 

 cular scar which is elongately semi-ovoid, externally with a convex and internally 

 with a concave margin. The valves are narrow and high about the middle, 

 somewhat compressed near the umbones, both of which are curved, and internally 

 provided with the usual ligamcntal groove. 



Localities. — South-east of Ootacod, near Valore (rare) ; near Poudicherry 

 (common), in a whitish or bluish grey sandstone. 



Formation. — Arrialoor group. 



The species is a characteristic fossil of the upper cretaceous beds (Campanien 

 apud Coquand) of almost all parts of the Avorld. It has been found all over 



* EiTore-tj'pico O. tigulaaa et tegulutea apud Coquand, Monog. Ostr. cret., pp. 58 et 212. 



