RHIZCSOLENIA. 415 



process terminating in a very long delicate bristle, generally curved. Breadth 

 of frustule, 1*5 to 2 c.d.m. Usually only fragments of this form are found. 



Marine. Rare. Blankenberghr. and basin. Coasts of England (Brightwell, Stolt., Kitton, 

 Norman, Baddelev, Wallick). Scotland (Baxter Coll., No. 2691). Ireland (O'Meara). Kattegat 

 (Cleve). 



R. Calcar-avis Schultze (Mull. Arch., 1858, p. 339, pi. 13, f. 

 5-10; Per., p. 113, pi. 4, f. 9-10*), plate 33, fig. 884. 



Frustules usually solitary, rarely united in threes, cylindrical, of rather 

 large size, with calyptra terminating in'a robust mucro, curved like a spur. 

 Frustules very delicately silicious, with annulation scarcely visible. 



Marine. Heligoland (Max Schultze). England (Norman). Ireland (O'Meara). Mr. 

 Peragallo says that this species is wide spread, but that it is overlooked in preparations and is 

 easily destroyed by acids. It is only distinctly visible when its endochronie is present. 



R. styliformis Brightw, (Q.J.M.S., 185S, vi., p. 94, pi. 5, f. 5 ; 



H.V.H. Ath, pi. 78, f. 1-5 ; pi. 79, f. 1, 2 and 4* ; Type No. 442), plate 

 17, fig. 601. 



Frustules sub-cylindrical, about 6 to 20 times longer than broad, formed of 

 distinct joints, surface covered with decussating strias, about 20 in 1 c.d.m., 

 terminating in a calytriform spathulate process, bifid at the base, the upper 

 part finishing in a straight, stiff process. Breadth of frustule, 2 to 4 c.d.m. 

 Length, very variable. Silica robust. 



Marine. Rather rare in Belgium ; Blankenberghe and basin. England (Brightwell, Kitton, 

 Baddelev, Norman, Stolt.). Scotland (Baxter Coll., No. 2691). Ireland (O'Meara). 



R. imbricata Brightw. (Q.J.M.S., 1858, vi., p. 95, pi. 5, f. 6; 

 H.V.H. Atl., pi. 79, f. 5-6* ; Perag., p. 113, pi. 5, f. 2-3), plate 33, fig. 885. 



Frustules cylindrical with section elliptical ; calyptra furnished with a 

 small and robust mucro ; annuli covered with coarse stria;, finely divided 

 transversely (analogous to those of the Radioseae) inflected on each side of 

 the median line or pseudo-raphe of the scale ; lines of imbrication lateral, 

 straight, very distant in each pair, silica robust. 



Marine. Coasts of England (Brightwell ? Kitton, Norman, Baddeley). Scotland (Baxter Coll., 

 No. 2691), Surface of River Dee (Stolt.). 



var. Shrubsolii (/?. Shrubsolii Cleve ; H.V.H. Atl., pi. 79, f. 11-13*), 

 plate 33, fig. 886. 



Only differs from the type-form by its narrower diameter. 



Marine. England (Norman, Kitton), Mouth of the Thames (Shrubsole). Excessively 

 common and abundant in the Scheldt. 



