CYCLADJE. 285 



ing to watch, under a low power of the microscope, 

 the striking and rapid changes of form through which 

 it passes in a short time. 



Mr. Jenyns tells me that latter research has in- 

 duced him to believe that vars. 1. and 3. are a distinct 

 species, for which he would retain the name of pulchel- 

 lum, while I would propose the name of P. Jenynsii 

 for the other varieties. 



119. 5. I* isi diu m Henslozviajium. Appendaged Pera. 



(t. 1. f. 6.) Shell obliquely oval, ventricose, finely 



striated ; umbones rather acute, with a laminar 



projection. 



Pera Henslowiana. Leach, MSS. 



Tellina Henslowiana. Leach, MSS. ; Shepp. Linn. 



Trans, xiv. 150. 

 Pera appendiculata. Leach, MSS. Brit. Mus. 

 Cyclas appendiculata. Turton, Man. ed. 1. 1. 15. £ 6. 

 Pisidium Henslowianum. Jenyns, Mon. 20. t. 21. 



f. 6, 7. 

 Inhab. rivers and ponds. 



Animal white ; siphon short, rather variable ; 

 generally rather conical and truncated. 



This shell is easily known by the curious eave-like 

 projections on the umbones, which are evidently 

 formed on the edge of the very young specimen, and 

 then gradually rise to the umbo as the shell in- 

 creases in size by the addition of new laminae of shelly 

 matter to its edge. 



120.6. Pisidium amnicum. (t. l.f. 5.) Shell ovate, 

 ventricose, deeply sulcately striated; umbones 

 rather blunt. 

 Tellina amnica. Miiller, ii. 205. ; Linn. Trans, 



