SURIRELLA. 373 



a a. COST.E MARGINAL, OR VERY DELICATE AT THE MIDDLE OF THE VALVE 



S. ovalis Breb. (Kiitz. Baa, p. 61, pi. 30, f. 64; H.V.H. Atl., pi. 

 73, f. 2* ; Type No. 425), plate 13, fig. 585. 



Valve oval elliptic or ovate, with costa? marginal, short, narrow, 5 in 1 

 c.d.m. Pseudo-raphe narrow. Striae rather delicate, 18 in 1 c.d.m. Girdle 

 face slightly cuneate, with alas indistinct. Length, 5 to 8 c.d.m. 



Fresh and brackish water. Brussels (Del.), Antwerp. Found everywhere. 



var. Crumena. (S. Crumena Breb./; H.V.H. Atl., pi. 73, f. 1*; Type 

 No. 424), plate 13, fig. 586. 



Valve almost disciform. Pseudo-raphe very narrow. 



Fresh and brackish water. Antwerp, common in the Scheldt. La Hulpe, Brabant 

 (Del.). England (Comber, Norman, Stolt.), Scotland (Arnott. in Baxter Coll. 2686), 

 Ireland (O'Meara). 



var. ovata. (S. ovata Kiitz. ; H.V.H. Atl, pi. 73, t. 5-7*; Type No. 

 426), plate 13, fig. 587. 



Smaller than the type-form (4 to 5 c.d.m.), and quite ovate. In a 

 form from the Scheldt (fig. 587, two right-hand figures), the costae are 

 prolonged up to the median line, while becoming gentlv thinner. 



Same stations. Rather common. 



var. minuta. (S. minula Breb. ; H.V.H. Atl., pi. 73, f. 9-14* ; Type 

 No. 428), plate 13, fig. 588. 



Still smaller than the preceding variety (2 to 3 c.d.m. in length), and 

 more elongated, with costae generally delicately prolonged as far as the 

 median line. 



Same stations. 



var. salina. (S. salina IV. Sm. : H.V.H. Atl., pi. 73, f. 15*; Type 

 No. 431), plate 13, fig. 589. 



Valves oval elliptic ; costae 5 or 6 in 1 c.d.m. 

 Brackish water. Antwerp, in the Scheldt. England (W. Sm.). 



var. angusta. (S.angusta Kuiz. : H.V.H. Atl., pi. 73, f. 12*; in Type 

 No. 430), plate 13, fig. 590. 



Valve very narrowly oval, linear, or sometimes panduriform, with 

 rounded apices. Length, 3 to 5 c.d.m. 



Fresh water. Koekelberg (Del), Aid. Lieg. (De Wild.) 



var. pinnata. (S. Pinna/a W. Sm. ; H.V.H. Atl., pi. 73, f. 13*; Type 

 No. 429), plate 13, fig. 591. 



Valve linear, narrow, with apices cuneate. Mean length, 4 to 5 c.d.m. 



Fresh water. Laeken (Del.), England (W. Sm., Arnott in Baxter Coll., 2793). 



All these forms, which are connected with one another, cannot be specifi- 

 cally separated. 



