BIDDULPHIA. 471 



Valve elliptic, with undulate margins, undulations 3 to 7, each of which 

 arise at one of the costae. Valve with cellular structure, cells arranged in 

 concentric rows round the centre of the valve, becoming gradually smaller as 

 they approach the centre, where there are 2 to 3 short horns generally awl- 

 shaped, sometimes capitate ; processes punctate, puncta becoming gradually 

 finer towards the apex. Girdle face subquadrangular, showing at the apices 

 undulations on a level with the valve, each of which corresponds with one of 

 the costae ; connecting zone with small cells arranged in straight lines (about 

 5 to 6 in 1 c.d.m.), interrupted by some irregular hyaline lines. Length of 

 valve, 5 to 17 c.d.m. Breadth, 6 to 9 c.d.m. at the median portion. 



Marine. Found only once in Belgium in the washing of mussels, but it will probably be found 

 more abundantly, as it exists on all the coasts of the North Sea. England (Ralfs, Griffiths, W. 

 Sm., Bleakley). Ireland (O'Meara). Scotland. 



II. Valves without costcz. 

 a. Valves furnished with processes in the form of spines. 



B. Regina, W. Sm. (S.B.D., ii., p. 50, P i. 46, f. 323; H.v.H. 

 Atl.,pl. 98, f. 1*), plate 34, fig. 894. 



Valves lanceolate, with undulate margins, showing three unequal compart- 

 ments between the processes. Girdle face with deep constrictions, which 

 divide the valve into three portions, mammiloid, hemispherical, with coarse 

 puncta arranged in regular lines, intermixed with small short spines. Processes 

 short, obtuse, mammiloid, with puncta becoming gradually finer towards the 

 apices. Connecting membrane with medium-sized scattered puncta. Breadth 

 of valve, 8 to 15 c.d.m. 



Marine. Isle of Skye (W. Sm.). Guernsey (Wallich !). 



B. Tuomeyi Bail. (Am.j.s., 1843, p. 138, f. 3-4; H.v.H. Atl., 

 pl. 98, f. 2-3*), plate 34, figs. 895, 896. 



This species differs essentially from the preceding, first, by the median 

 compartment being considerably more elevated than the two lateral, and 

 surmounted by 2 to 3 long spines, and next by the processes which are elongated, 

 narrow, refiexed and inflated at the apices. 



Marine. This form, so far as I know, has never yet been found on our shores. I only mention 

 it in consequence of some authors having considered that the preceding species is only a variety 

 of B. Tuomeyi. The examination of numerous specimens does not enable me to agree with this 

 opinion. 



B. aurita (Lyng.) Breb. (Consid. sur les Diat., 1838, p. 12; 

 H.V.H. Atl., pl. 98, f. 4-9* ; Type No. 488), plate 20, fig. 631 



