ODHNUR : ON I'ISIDIUM IN 'I'HH SWEDISH STATE MUSEUM. 223 



Norway : Without definite locality (Esmark, det. by Clessin as 

 obtnsale). 



Finland : Lake Etiare (Malm), some large specimens (length 3 

 mm.). This locality is of special interest since it proves that P. hiber- 

 niciim occurs far towards the north. 



Pisidium personatum Malm, 1855. 



I have not had any opportunity of examining the soft parts of this 

 species, and therefore cannot express any opinion about its atilinities 

 and specific validity ; but it seems to be distinct in shell characters. 

 The latter have been established in an accurate manner by Woodward 

 (1913), who has drawn attention to the callosity in front of the pos- 

 terior laterals as the chief characteristic of the species. This feature 

 is well marked in the type, as I have convinced myself by examining 

 Malm's originals. 



The species seems very rare in Sweden ; it has been collected only 

 at Gothenburg in Halland (Malm), and at Visby, Gottland. 



Pisidium pusilium of B. B. Woodward. 



In a paper " On the Pisidium nitidiun and P. pusilium of Jenyns : 

 a Reply" {^Journal of Conchology, 19 18), Woodward has quoted a 

 statement of mine, and referred this to his P. pusillwn. He says : — • 

 " This species as identified by me . . . shows a peculiarity in its gill- 

 structure in both deep and shallow water forms." This statement, 

 however, should refer to the species which I described in 1908 as 

 P. iornense, and which has erroneously been identified by ^Voodward 

 with P. pusilluDi Jenyns. It is quite a distinct species, as shown 

 above (v. P. clessini). 



I think Stelfox is correct in regarding P. pusilium of Woodward, 

 with this exception, as identical with P. iiitidum Jenyns. It is not 

 easy to distinguish between the two species in Woodward's sense, and 

 they cannot be separated either by their shell characters or by their 

 anatomy. Mr. Woodward has kindly sent me specimens named by 

 him P. pusilium, as well as some named P. tiitidufu, the latter 

 exactly similar to specimens forwarded by the older English naturalists 



o 



(e.g., Alder). In examining large series of Pisidia from Lake Takern, 

 I have failed in my attempts to allot the specimens to one or other 

 of Woodward's forms ; on the contrary, I have found frequent tran- 

 sition between them. It may be stated that in the specimens received 

 from Mr. Woodward as iypicaX pusilium, two gills on each side could 

 easily be seen, in spite of their dry state. 



Malm's P. pusilium is quite another species, namely P. casertanuui, 

 according to original specimens which I have examined. 



