M'KCIKS OF I'ISIDIU.U. 7 



not adequate, still it sufficiently fits the form to which 

 Jenyns subsequently applied it. 



Lamarck's other two species referable to Pisidium are: 

 Ci/clas obliqua ( = Pisidinm amnicum) and Ct/clas fontinalis. 



1821. C. Pfciffer (134) defined the genus Pisidium and placed in 

 it : 1. P. obliquum (Lam.), 2. P. obtusale (Lam.), and 3. 

 J\ foHftiiah (Dnip.). It is doubtful if the latter were the 

 same as Draparnaud's species, and the descriptions and 

 figures are equally vague. 



1825. Sheppard (163) discovered and named Tellina henslowana. 

 His characterization leaves no doubt as to his species, which 

 i.s never questioned. 



1832. Jenyns published his classical memoir (83) from which dates 

 our present knowledge of the British Pisidia. He detected 

 two additional species, and had he only been aware of the 

 value of the hinge-characters, would certainly have added 

 more, for some of his species undoubtedly combined more 

 than one form. His descriptions are full, but the figures, 

 though beautifully drawn, are not accurate representations 

 from the scientific point of view, as a careful comparison 

 of them with original specimens at Bath showed. His 

 species were : 



1. P. obtusale, Pfeiffer. 



2. P. pusillum, nobis.* (The extreme variety fig. 5 



would probably, could it be 

 opened, prove to be P. per- 

 sonatum.) 



3. P. nitidum, nobis. 



* 4. P. L rukheUam, nobis , ^^ ^^ tQ be wom 



I \ examples of the oval form 

 " 



var. 2. (This, as well known, proved 



to be P. milium, Held.) 



5. P. hcntlowianum, nobis.* 



var. /3. (This was a perfect speci- 



men of P. subtriincatum.) 



6. P. amnicum, nobis.* 



Jenyns, when he wrote his paper, was not acquainted 

 with the form here designated P. casertanum, but his 

 collection contains specimens of P. cinereum, Alder, sent 

 him by that naturalist, as well as P. yibba (seemingly an 

 oval form of P. nitidum) and P. fortitude (= subtrun- 

 calum), both from Alder, who in 1838 put them in Jenyns' 

 pusillum. 



* Jen yns adopted the current botanical method of nomenclature in which 

 the name' of the author of the complete name, and not of the species only, is 

 given. The authors of the species appear in the synonymy. 



