372 SURIRELLA. 



S. Gemma Ehr. (Abh., 1840, p. 76, pi. 4, f. 5; H.v.H. Atl., pi. 74, 



f. 1-3* ; Type No. 433), plate 13, fig. 582. 



Valve more or less longly oval, with costae indistinct, about 2 to 3 in 1 

 c.d m., reaching to the median line, which is narrow ; strice fine, transverse, 

 20 or 21 in 1 c.d.m., resolvable into beads in appropriate illumination. 

 Girdle face strongly cuneate, alae marginal, scarcely visible. Length, about 7 

 to 12 c.d.m. 



Marine. Blankenberghe, Antwerp (Scheldt, H.V.H.) Common on all our coasts. 



A A. Costae marginal or becoming gradually fainter. 

 a. COSTAE VERY ROBUST ON THE MARGIN OF THE VALVES. 



S. fastuosa Ehr. (Abh, 1S41, p. 19; h.v.h. Atl., pi. 73, f. 18*; 



Type No. 432), plate 13, fig. 583. 



Valves broadly oval ; costse very robust at the margin, but gently diminish- 

 ing in breadth as far as the third of the valve where they leave a space 

 lanceolate, bordered with elongated dots, and sometimes they continue in this 

 space, but in doing so they become more delicate. Pseudo-raphe narrow. 

 Striae delicate, about 19 in 1 c.d.m. Girdle face cuneate, with rounded 

 margins, showing robust alas, approximate to the connecting zone. Length, 5 

 to 12 c.d.m. 



Marine. Washings of mussels (Deby), Blankenberghe, Scheldt. (H.V.H. ), England (W. Sm, 

 Comber, Norman, Stolt,), Ireland (O'Meara), Scotland (Arnott in Baxter Coll. 2546, 2764). 

 Very numerous forms there as well as on all our shores. 



var. lata. (S. lata IV. Sm.; H.V.H. Atl, pi. 73, f.17*), plate 13, 

 fig- 584- 



Differs from the type-form by its larger size, and by the median con- 

 striction of the valves. 



With the preceding. Scheldt (H.V.H.), England (Comber, Ralfs.), Scotland (William- 

 son), France (Breb.), 



The innumerable forms of S. lata have been raised by some authors to 

 the rank of species. Gregory has further recorded intermediate forms, which 

 connect S. fastuosa with S. lata. 



S. turgida W. Sm. (S.B.D,i,p.3i,pi. 9 ,f. 60*), plate 31, fig. 867. 



Valve elliptic, oval, with apices sub-obtuse or slightly acute ; median 

 portion much inflated; costoe robust, shortened, about 1-25 in 1 c.d.m.; 

 pseudo-raphe much enlarged, lanceolate. Length, 7 to 12 c.d.m. 



Fresh and brackish water. England (Norman, Carrington), Ireland (Dickie). 



