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 1 would propose the name of 
P. Jenynsii for the other varieties. 
124 . 5. PismiUM 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.; Forhes and Hanley., B. M. 
ii. 131. t. 37* f. 11.; Shepp. Linn. Trans. 150. — Pera 
appendiculata. Leach., MSS. Brit. Mus.., Syn. Moll. 292. — 
Cjclas appendiculata. Turton., Man. ed. 1. t. 15. f. 6. — 
— Pisidium Henslovvianum. 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, andP. Tando- 
nianum. Cess. Nouv. Pisid. 6. — P. Dupuyanum. Norman^ 
Cycl. 5. — P. Becluzianum. 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 
