414 RHIZOSOLENIA. 



Mr. Peragallo divides the Rhizosolenix into three groups, which we adopt 

 here, viz. : 



GROUP I. Annulate? . Frustules annulate. 



R. robusta Norm, (in Pritch. Inf., p. 866, pi. 8, f. 42 ; Perag., pi. 2, f. 

 1, and pi. 3, f. 1-2*), plate 33, fig. 883. 



Frustule cylindrical, depressed ; section elliptic, axis curved, hood consist- 

 ing of annuli with antero-posterior imbrication confused, mucrones very 

 small ; annuli of frustules flat, finely striate, lines of an antero-posterior 

 imbrication straight and opposite ; silica rather delicate, size variable but 

 always considerable (H. Per.) 



Marine. North Sea (Norman). Teignmouth, Devonshire (stomach of Phallusia W. Arn. !) 



GROUP II. Sqnammosce. Frustules formed of scales, more or less 

 rhombical, very numerous and giving a squamous appearance to the 

 frustule. 



We have no form belonging to this group within the limit ol the North 

 Sea. 



GROUP III. Genuine^. Frustules formed of rhombical scales 

 arranged usually in two but never exceeding four rows. 



ANALYSIS OF SPECIES. 



Valve furnished with a long bristle (seta) . . . . R. setigera. 



f Mucro long and very robust, curved like a spur . R. Calcar-avis. 



I 



f Scales showing coarse inclined 



Valve furnished . . striae, finely divided trans- 



it, "1 Mucro short, \ J -r, jt,_j + 



J - with a mucro. . ,. ' j versely . . . R. lULDricata. 



straight, 



broad. 



I Scales fine ; puncta in quincunx, 



visible with difficulty . R. styliformis. 



Valve with a rather long calyp.tra, attenuate, flattened, without seta or 

 mucro . . . . . . , R. alata. 



R. setigera Bright w. (Q.J. M.S., 1858, vi., p. 95, pi. 5, f. 6; 



H.V.H. Atl., pi. 78, f. 6 and 8*), plate 17, fig. 602. 



Frustule sub-cylindrical, about 5 to 15 times longer than broad, joints 

 only visible in oblique illumination. Striae excessively delicate ; calyptriform 



