BIDDULPHIA. 475 



b. Valves without spines. 

 * VALVES WITH CELLULAR STRUCTURE. 



B. antediluviana (Ehr.) H. Van Heurck. (Amphitetras 



Eh*-. ; H. V.H. Atl, pi. 109, f. 4 and 5* ; Type No. 501), plate 21, fig. 642. 



Valve quadrangular, with margins straight or concave, centre depressed, 

 four robust processes, finely punctate ; structure cellular, cells in concentric 

 circles, allowing the puncta of the inferior layer of the valve to be slightly 

 seen in the transparent portion. Girdle face quadrangular, with valves 

 constricted near the sutural zone. Connecting membrane with coarse puncta 

 forming irregular longitudinal lines, about 4 to 5 in 1 c.d.m., interrupted by 

 transverse hyaline spaces. Frustules forming bands, generally in zig-zag. 

 Length of valve, 2*5 to 14 c.d.m. (in the latter measurement the concavity of 

 the valve has not been substracted ; from one excavation to another, the 

 length would not be more than n c.d.m.). 



Fossil. Potter's clay at Ostend ( Oeby). Found not only on all the Coasts of the North Sea, 

 but also on all the Coasts of Europe, America, etc. England (W. Sm., Okeden, Ralfs, Griffiths, 

 Kitton), Orkney Islands (Baxter Coll., No. 3111, 3112), Ireland (O'Meam), Guernsey (Baxter Coll., 

 No. 3114). 



var. pentagona. (Amphipentas Ehr.). Valve with five angles. 



Not yet found in Belgium. England (Hodgson), Scotland (Hennedy). 



B. Favus (Ehr.) H. Van Heurck. {Tricer atium Favus Ehr.; 

 H.V.H. Atl., pi. 107, f. 1-4* ; Type No. 500), plate 21, fig. 643. 



Valve triangular, with centre convex ; three terminal processes robust, 

 elevated, finely punctate up to the ends ; sides straight or somewhat convex. 

 Structure with coarse hexagonal cells allowing the fine puncta of the inferior 

 surface of the valve to be seen. Partitions of the cells embellished with 

 small spines. Length of girdle face much greater than the breadth ; con- 

 necting zone delicately striate lengthways (about 16 striae in 1 c.d.m.), with 

 puncta in quincunx. Length at the margin of a valve of medium size, 9 to 15 

 c.d.m. 



Marine. Rather common. Blankenberghe, Ostend, Antwerp (Scheldt), and found almost 

 everywhere. England (Shadbolt, Hodgson, Kitton, Stolt. , Norman, Comber). 



* VALVES PUNCTATE, NOT CELLULAR. 



B. alternans (Bail.) H. Van Heurck. (Trkeratium aiter- 



nans Bailey ; Mic. Observ., South Carol.; H.V.H. Atl., pi. 113, f. 4, 5 and 

 7*; Type No. 505), plate 21, fig. 644. 



