CYCLAD^. 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 ofpulchel- 

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

 for the other varieties. 



119. 5. PISIDIUM Henslowianum. 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. 1. f. 5.) Shell ovate, 

 ventricose, deeply sulcately striated; umbones 

 rather blunt. 

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



