10 



CATALOGUE OF 



1857. Uaudon, the French Jenyns, in his careful " Essai " (9) 

 made partial use of the hinge for classification, but did not 

 avail himself of its details for the distinction of species, of 

 which he specified eight : 



1. P. olttusale. 5. P. casertanum. 



"2. P. pusillum. 6. P. amnicum. 



3. P. nitidum. 7. P. henslowanum. 



4. P. gassiesianum [ = milium~\. 8. P. conicum [=.supinum~\. 



He included the whole of Jenyns' P. pulchellam under 

 P. casertanum. Unfortunately Malm's work was not 

 known to him. 



1858. Jenyns published some notes on the smaller species (84) in 



which he modified certain of the conclusions he had 

 come to in his Monograph. He had received five specimens 

 agreeing exactly with his P. hensloivianum except in being 

 entirely destitute of the lamelliform projection on the 

 umbones, and was at first doubtful whether to refer them 

 to P. Jtenslowanum or P. pulcliellum. It has been pointed 

 out that in the case of both these species Jenyns had 

 included specimens of P. subtruncatnm to which obviously 

 the new finds belonged, and since he never made any 

 distinction, as is done to-day, between the type and varieties 

 of a species, he came to the conclusion that his P. hens- 

 lowianum and P. pulchellum should form one species, and 

 since the former was the older name it should " in future 

 be adopted as the general name for this species/' He 

 further considered the normal form of P. henslowianum thus 

 constituted would be that with out the appendicula? (p. 105), 

 and added (p. 106) that " if it be thought desirable still to 

 retain a name for that variety which is so peculiarly dis- 

 tinguished by the umbonal appendages it might be called 

 var. appendiculata" 



This forcible dethronement of Sheppard's type, in which 

 the Jippendiculae formed its salient character, cannot of 

 course be entertained. 



Jenyns also remarked in this paper (p. 106) " I am 

 inclined to think that the P. pusillum and P. cinereum are 

 not distinct." 



He further cautioned collectors against deciding hastily 

 on any of these small bivalves, adding (p. 107): "This 

 remark applies especially to the P. nitidum, which in general 

 form is so similar to the P. pusillum." 



1859. Early the following year Jeffreys, in his " Further Gleanings " 

 (80), published for the first time his conclusions as to the 

 species of Pisidium* These he reduced to five in number, 

 viz. : 



* He had already communicated them in the previous November to Jenyns, 

 as shown by extracts kindly made for me from the Jenyns Correspondence at 

 Bath by Major M. Connolly. 



