PISIDIUM. 267 



The siphonal tube assumes a variety of appearances 

 even in the same individual ; and it is very interest- 

 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 later research has in- 

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

 tinct species, for which he would retain the name of 

 P. pulchellum,, while I would propose the name of 

 P. Jenynsii for the other varieties. 



124. 5. PISIDIUM Henslowianum. Appendaged Pera. 

 Shell obliquely oval, ventricose, finely 

 striated ; umbones rather acute, with a laminar 

 projection ; cardinal teeth not prominent, ru- 

 dimentary, imperfectly disposed in a reversed 

 V; lateral teeth large and thick, (t, 1. f. 6.) 



Pera Henslowiana. Leach, MSS. Tellina Henslowiana. 

 Leach, MSS., Syn. Moll. 291.; Forbes and Hanley, B. M. 

 ii. 131. t. 37. f. 11.; Shepp. Linn. Trans, xiv. 150. Pera 

 appendiculata. Leach, MSS. Brit. Mus., Syn. Moll. 292. 

 Cyclas appendiculata. Turton, Man. ed. 1. t. 15. f. 6. 

 Pisidium Henslowianum. Jenyns, Mon. 20. t. 21. f. 6, 7.; 

 Moq. Tand. Moll. Franc. 581. Pisidium acutum. Pfeiffer, 

 in Wiegm. Arch. 1831, 230. Pisidium pallidum. Gass. 

 Pisid. Aquit. t. 1. f. 10. P. Bonnafouxianum, and P. Tando- 

 nianum. Cess. Nouv. Pisid. 6. P. Dupuyanum. Norman, 

 Cycl. 5. P. Recluzianum. Bourg. Jour. Conch. 1852, 174. 

 t. 8. f. 8. 



Inhab. rivers and ponds. 



Animal white; siphon short, rather variable, 

 generally rather conical and truncated, entire. 



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 



