304 Mr Jenyns's Monograph on the 



the anterior extremity still being in a slight degree longer than the 

 posterior. It is by no means of uncommon occurrence, residing chiefly 

 at the bottoms of drains and ditches, where I have often found it 

 buried at a considerable depth in the soft mud. It appears to be some- 

 what amphibious in its habits. Nilsson observes that it is often to be 

 met with between the bark and the wood of decayed timber in wet 

 places, and I have myself noticed that in confinement it will frequently 

 leave the bottom of the vessel, and ascending the sides, take up its 

 residence immediately above the edge of the water with its shell wholly 

 exposed. It is a tranquil species, seldom moving much about, and 

 never walking on the under side of the surface of the water. Where 

 it occurs at all, it is generally in profusion. 



Dr Leach appears to have raised this species to the rank of a distinct 

 genus, under the name of Euglesa, but it hardly shows sufficient 

 peculiarities to warrant this step. The shell is certainly somewhat in- 

 termediate in form between that of Cyclas and Pisidium. 



Sp. 3. P. nitidum, Nobis.— Tab. xx. Fig. 7, 8. 



P. testa, orbiculato-ovali, nitidissima, tenuiter striata ; umbonibus obtu- 

 siusculis, striis paucis profundioribus. 



Long. 1^ lin. Alt. vix l|lin. Crass. 1 lin. 



Animal album ; siphone brevi, infundibuliformi, apertura patula, plus 

 minusve margine crenato, plicatulo. 



Testa minime variabilis, orbiculato-ovalis, parum inaequilateralis ; prasce- 

 denti paul6 convexior, et pro ratione longitudinis altior ; albo-lutescens, 

 nitidissima, raro aut nunquam sorde aut rubigine obtecta, tenuiter 

 striata, striis hie illic, prascipue 3 — 5 umbones transeuntibus, dis- 

 tinctius incisis : umbones obtusiusculi, dorsalem marginem paulo supe- 

 rantes. 



