282 Prof. A. Leymerie on the Lower Greensand 



To convince the Society of this, it will suffice to recall here 

 the principal differential characters which led me, in 1842, to 

 consider the species in question as new ; characters the ma- 

 jority of which had already been indicated in the short de- 

 scriptions annexed to my memoir. 



Pholadomya Prevostii Desh., differs from the Mya plicaia, 

 Sow., by an abrupt inflection which it bears on each of its 

 valves, close to the posterior margin, by its more oblong form, 

 diminishing more rapidly in height from one extremity to the 

 Other. Moreover the species of Sowerby is a Panopcea, ac- 

 cording to M. Deshayes, whilst that of I'Aube belongs to the 

 genus Pholadomya. 



Astarte Beaumo?itii, Leym. — According to the figures, the 

 idea would not occur to any one to compare this species with 

 the Astarte obovata, Sow., which is much less depressed {bien 

 plus haute), more equilateral and subtruncated. The descrip- 

 tion of the English author is moreover not sufficiently explicit 

 to lead to any conclusion. 



Cardium subhillaniim, Leym. — I have indicated in my text 

 the characters which separate this species from the Cardium 

 striatidum. Sow., which toward the middle of its valves has 

 only concentric striae, whereas in ours the principal striae are, 

 on the contrary, longitudinal. 



CucullcBa Gabrielis, Leym. — We have pointed out with so 

 much care the important differences which separate this spe- 

 cies from the Area exaltata, Nilson, that we cannot but think 

 that Mr. Edward Forbes has not consulted our text before 

 deciding on assimilating two such different shells. 



Pinna sulci/era, Desh. — The characters by which this Pimia 

 is distinguished from the Pitma tetragona, Sow., are so ob- 

 vious and so easy to be perceived at the first glance, that we 

 are very much surprised that Mr. Forbes should have mis- 

 conceived them so far as to confound these two shells. In 

 fact, besides the general form, which is very different, our spe- 

 cies has round and well-marked costse, separated by well- 

 marked furrows, whereas the Pinna tetragona, Sow., only ex- 

 hibits slight striae. 



Pecten interstriatus, Leym. — This Pecten is principally cha- 

 racterized by the striae which cover the intervals of the costae, 

 stria2 which do not exist in the Pecten obliquus, Sow. This 

 last species has moreover costse much more distant from each 

 other, and a very different general form. 



Modiola ArchiacifLieym. — We might perhaps condemn this 

 species, which much resembles in fact the Modiola ccqualiSf 



