Von Koenen — Belgian Tertiaries. 501 



flat, sloping, striate continuously with the ribs of the disc ; no very distinct anterior 

 area. Teeth very prominent. 



This easily distinguished and handsome little species is related to the recent 

 L. jamaicensis. It is without the large well-defined, anterior dorsal area which that 

 species seems to have. It is also allied to L. ornata, D'Orb. 



Upper Miocene, Jamaica. 



YI. — Leda incognita. (Fig. 1.) 



Shell transversely-ovate, compressed, with rounded concentric ribs ; rostrated pos- 

 teriorly. Dorsal areas broad, distinct, circumscribed by the keels which run from the 

 umbones to the extremities. 



Lower Miocene, San Fernando, Trinidad. 



VII. — Madra suhovaUna. (Fig. 6.) 

 Shell triangularly sub-oval, transverse, nearly equilateral, rather thin, compressed, 

 concentrically striate by lines of growth ; posterior slope large, and well-defined by 

 the keel running from the umbo to the posterior end ; anterior slope smaller, and less 

 defined, the carina tion running from the umbo becoming obscure towards the 

 extremity. 



This belongs apparently to the group of true Madras, of which the British 

 M. stultorum is an example, somewhat allied to the present shell. 

 Lower Miocene, San Fernando, Trinidad. 



V. — On the Belgian Tebtiakies. 

 By Dr. A. von Koenen, of the University of Marburg. 



SINCE Sir Charles Lyell published his most accurate and detailed 

 paper " On the Tertiaries of Belgium and French Flanders," geo- 

 logists could only differ in their opinions on the facts mentioned by 

 him. New discoveries have been made in Belgium only in the last 

 few years ; besides the splendid cuttings in the ditches for the forti- 

 fication of Antwerp, about which I am going to speak afterwards, 

 there has been found, near Mons, by sinking a well, a thick bed 

 of lime and limestone at the base of all hitherto-known Belgian 

 Tertiary beds, containing numerous and well-preserved Tertiary 

 marine and fresh- water moUusca. The discoverers, MM. Cornet and 

 Briart, Engineers of Mines, and most zealous geologists, described 

 very carefully the geological position^ and afterwards the extension'^ 

 of these lowest Tertiary beds in Hainaut. In their first paper they 

 had tried to determine the Molluscan fauna of this basement bed, 

 after Deshayes' works ; but, out of 150 species, they could name 

 only 22, and amongst these there are still some very doubtful ones. 

 These 22 species, belonging to beds superior to the " Glauconie 

 inferieure " and to the "Sables de Bracheux" of the Paris basin, 

 they concluded that the new beds at Mons corresponded in age 

 with a part of the " Calcaire grossier," and with the Upper part of 

 the " Sables inferieurs " (Cuise-la-Motte). 



Now the Calcaire grossier and the Sables de Cuise contain a very 

 rich and well-known fauna, so that I concluded,^ from the small 

 number of species identical to them and to the beds of Mons, that they 

 were of different age, rather than of the same, and the fauna of the 



1 Bull, del Acad. roy. de Belg. 2me serie t. xx. No. 11 and t. xxii. No. 12. 



2 See also Geol. Mag., 1866, Vol. III. p. 174. 



3 Zeitschr. d. D. Geol. Ges,, six., pg. 32. 



