26o 



ON THE PISIDIUM NITIDUM AND P. PUSILLUM 

 OF JENYNS : A REPLY. 



By B. B. woodward, F.L.S., &c. 



(Read before the Society, Februar}' i3lh, 191S). 



It is an exceedingly old forensic and debating manoeuvre to misstate 

 a case for the sake of more easily demolishing one's opponent. 



Quite unintentionally, of course, this is the method adopted by 

 Mr. Stelfox in his paper recently read before this Society i^Journ. of 

 Conch., XV., 1918, pp. 235-239). Therein (p. 237) he gives a figure 

 of a specimen from the "Hyndman Collection" in the Belfast Muni- 

 cipal Museum of a Fisidhiin, which he states to be ^^Pisidium nitidiim 

 Jenyns (=/'. pusilliim (Jenyns) B. B. Woodward)." The first half of 

 this statement is perfectly correct, the second entirely false. Judged 

 by the drawing, which is obviously very good, this example further 

 confirms the conclusions I had drawn from the specimens at Bath, 

 and from the precisely similar example which Jenyns sent to Forbes 

 and Hanley to figure in their great work. It does not resemble my 

 idea of what should be selected as the P. pusilhiin of Jenyns in the 

 least, and Mr. Stelfox has not the smallest warranty for saying that 

 it does. 



As regards the question of P. pusillum, Jenyns' species was a com- 

 posite like his pulchellum, and, as his later paper (Ann. and Mag. Nat. 

 Hist., ser., iii., vol. ii., 1858, pp. 104-107) shows, most of his other 

 species. The idea of a " type " in its modern conception had not 

 been evolved in Jenyns' time, and for pnsilhim he figured " two ex- 

 treme varieties" (Trans. Camb. Phil. Soc, iv., 1832, p. 312), and not 

 one example, as would be inferred from the notes of Mr. Oldham, 

 quoted by Mr. Stelfox. One of these (fig. 5) as I pointed out (Cat. 

 Brit. Pisidiiun p. 7) would probably if opened prove to be P. per- 

 so7iatuin Malm. From an inspection of Jenyns' own collection, from 

 his later paper, and from specimens in my own and other collections, 

 traceable more or less directly to Jenyns, it is obvious that he had 

 also identified as his P. pusillutn specimens of P. cascrtanwn f. 

 lacustris. Eliminating this last and the P. personatum of Malm, there 

 remained a well-marked form, which as next reviser I selected as his 

 P. piisilluvi. This species as identified by me. Dr. Nils Hj. Odhner, 

 of Stockholm, informed me, shows a peculiarity in its gill-structure 

 in both deep and shallow water forms. It was unfortunately not 

 possible to quote this fact in my " Catalogue " because Dr. Odhner 

 intended to publish it himself Publication has, of course, now been 

 deferred, but his interesting results will, it is to be hoped, yet see 

 the light of day. P. pusilluvi, as I understand it, is common in 

 Ireland, and especially fine in the shell-marl deposits. That Mr. 



