A. DE BREBISSON ON SOME FRENCH DIATOIIACE^E. 89 



Wedel, another Surirella, the S. nobilis or robusta, the valves of 

 which are also armed with a spur. It is the S. splendida (?) var. 

 aculeata of M. Grunow. Then, finally, I found again near Falaise, 

 a real S. splendida, Ehrenb., on the valves of which is also seen a 

 rudimentary spur. This appendage is not, therefore, an essential 

 characteristic, on which we can establish a distinction of species, 

 but only an accidental state, the result of a superabundance of silex 

 in a certain point of the carapace of these Diatoms. Often in 

 such a case, a collection of the siliceous matter, the secretion of 

 which forms the envelope of the Diatornaceaa shows itself on the 

 middle of the valves, in the form of a kind of cord, or medial nerve. 

 This line, strengthened, may remain straight and salient, in con- 

 sequence of rupture in the point where the valve bends suddenly, 

 especially at the broad and rounded extremity of the cuneiform 

 frustules ; at the other summit, which is narrower and less curved 

 inwards, it is rarer to meet with such a spine-shaped appendage, 

 although this anomaly is sometimes met with there. 



The Surirella biseriata, which is also in these preparations, having 

 no decided curve at the summits of its valves is never furnished 

 with spurs. Nevertheless, this Diatom, although its envelope is 

 not cuneiform, is probably, like the preceding, only a modification 

 of one and the same type. 



Surirella linearis, W. Sin. and Sur. amphioxys, W. Sm. In 

 examining the different forms which are found mingled together in 

 these preparations, we might be tempted to believe that the draw- 

 ings given by W. Smith were made from a similar collection. 

 Several authors, and W. Smith himself, have remarked that the 

 figures 58a, a 1 and b 1 of the synopsis (t. 1., pi. viii.) belonged to 

 at least two species. In these preparations may be recognised 

 individuals which ought to be referred to the Sur. pinnata, the 

 S. panduriformis, and even to the S. angusta, which would assign 

 to all these forms one and the same point of departure, an hypo- 

 thesis which is very admissable. 



Surirella crumena Breb. (in litt. ad Kiitz., 1844, con. spec.) 

 Cyclotella Meneghiniana (3. major Spec. Alg. p. 19. Surir. Bright 

 wellii, W. Smith, syn. i., p. 33, pi. ix., f. 69.(?) Fresh and brackish 

 waters, Calvados, Geneva, Montpellier, etc. Misled by a form of 

 Sur. subsalsa with large valves and rounded, which I refer to fig. 

 G9, pi. ix., of W. Smith's Synopsis, I thought that as this figure 

 represented >,he type of *S*. Brightwellii this species ought to be 



