12 



RANDOM NOTES ON NATURAL HISTORY. 



mudd}' streams. Several j^ears ago, when 

 the water of the Blackstoue River was 

 drawn off at Pawtucket, I examined the bed 

 of the river, just above the upper dam, and 

 among several other species, was an abun- 

 dance of these shells buried in the mud, 

 where, under ordinar}' circumstances, their 

 existence would not be suspected, or if so, 

 they could not be obtained, being under 

 several foet of water. Sometimes the}' are 

 found under shelving banks or in mud near 

 the margins of large ponds. They are 

 stout and solid shells, varying in color from 

 yellowish-green to dark olive. Our Rhode 

 Island shells have a uniform dark olive 

 green epidermis, and the apex is invariably 

 decollated. At Albany, N. Y., where Me- 

 lantho decisa and Integra live together in 

 the Hudson River, this species is alwa^'s 

 decollated, while the apex of Integra is per- 

 fect. They do not deposit ova like the 

 other fresh water snails, but retain the 

 3'oung within the shell, and when they make 

 their advent into the world they are pro- 

 vided with a shell of three complete whorls. 



All the shells thus far described in these 

 papers are marine or salt water species, ex- 

 cepting five species which are fresh water 

 shells. These five are water breathers and 

 live at the bottom of our ponds and rivers, 

 and are not obliged to come to the surface 

 to obtain a suppl}' of air. They are also 

 provided with an operculum, or door, with 

 which they close the mouth of the shell. It 

 is attached to the foot of the animal, and 

 when the animal retires into its shell, the 

 operculum is the last portion to go in and 

 completely closes the aperture. This oper- 

 culum is not composed of carbonate of lime 

 like the shells of mollusks, but of phosphate 

 of lime and animal matter, like the shells 

 of crabs and lobsters, and much resembles 

 horn. There are also very many other fresh 

 water snails, which breathe air and are not 

 furnished with an operculum. These belong 

 to a diflferent sub-class from those hereto- 

 fore described and from manj* others to 

 follow, but will be taken up in their order 

 at a future time. 



{To he continued. ) 



CHECK-LIST OF BRITISH FRESH-WATER SHELLS. 



J. RITCHIE, JR. 



Paludina contecta Millet. 



A'ivipara Linn. 

 Bythinia leachii Sheppard. 



tentaculata Linn. 

 Hydrnhia similis Drap. 



ulvse Penn. 



ventrosa Montagu. 

 Valratd cristata INIiiller. 



piscinalis Miiller. 

 Ncritina fluviatilis Linn. 

 LiiiuHfa auricularia Linn. 



glabra Mtiller. 



glutinosa Miiller. 



involuta Thompson. 



palustris Miiller. 



peregra Miiller. 



stagnalis Linn. 



truncatula Miiller. 

 Phy.sa fontinalis Linn, 

 hypnorum Linn. 

 Planorbis albus INIiiller. 



carinatus Miiller. 

 complanatus Linn, 

 contortus Linn. 

 Cornells Linn. 



Planorbis dilatatus Gould. 



glaber Jeffreys. 



lineatus Walker. 



nautileus Linn. 



nitidus Miiller. 



spirorbis Linn. 



vortex Linn. 

 Ancylv.s fluviatilis Miiller. 

 lacustris Linn. 



Sphcerium corneum Linn, 

 lacustre Drap. 

 ovale Fer. 

 rivicola Leach. 

 Psidium aranicum Miiller. 

 fontinale Drap. 

 nitidum Jen3'ns. 

 pusillum Gmelin. 

 roseum Scholtz. 

 Unio margaritifer Linn, 

 pictorum Linn, 

 tumidus Retz. 

 Anodonta anatina Linn, 

 cygnea Linn. 

 Dreissena polymorpha Pallas. 



