343 



Churchdown, I met with two shells that at first glance looked 

 like Ostrece, but which on reaching home, I at once determined 

 to be P. laevigata, both of them being left valves, and they were 

 bbelled under that name. 



I was led to this conclusion by the peculiar foldings of the 



lines of growth : they were not foliated like those of an Oyster, 



but were what the French express by the word contourves ; 



further, I was more particularly impressed by the peculiar 



triangular apex of the umbo, both leading characters of A. 



d'Orbigny's species. On afterthought, and being much influenced 



by the fact of the very restricted range of this particular 



fossil, a slight misgiving arose, for I deemed my determination 



unsafe in the absence of any knowledge of the hinge-area of 



my specimens. I, therefore, provisionally cancelled the name 



of P. Iwvigahis, and determined to carefully excavate the shell 



about the hinge margin of the specimen, which happened 



to be the left or free valve, never dreaming of the probability 



of meeting with the right or adherent valve, which would 



have cleared up the point. Accordingly, I had actually begun 



to cut away the layers of the shell, when I was forced to 



leave the work unfinished as the fossil was intensely hard; 



whilst it was left in this incomplete state, I went by 



chance some time after toward the quarry where the first 



examples were found, and the first object my eye detected 



was the right or adherent valve, with the teeth perfectly 



exposed, only slightly abraded by the sand-drift of- the 



marlstone; and adherent to a piece of thin-bedded micaceous 



marlstone of the Middle Lias. Now to shew how rare this valve 



is, even where the species exist in considerable numbers, I will 



quote the testimony of those able Paleontologists, M. M. 



DuMORTiER and J. A. Eudes Deslongchamps: the former declares 



that he has only met with the right valve ; and the other states 



that he has never met with it. M. Dumortieu says, " Malgre le 



tres grand nombre d'echantillons que j'ai pu examiner du 



Harpax Iwvigatus, je n'ai jamais rencontre la valve droite, ou 



adherente." J. A. Eudes Deslongchamps, "fait remarquer qu'il 



n'a jamais pu observer non plus que la valve gauche, ou libre, du 



