22 



RANDOM NOTES ON NATURAL HISTORY. 



The Shell-Bearing Mollusca of Rhode 

 Island. 



BY HORACE F. CARPENTER. 



Chapter XXVI. 



84. ZoNiTES (Punctum) minutissimum, Lea. 



Shell broadl}' umbilicated, sub-globose, 

 reddish horn color, shining, marked with 

 strong transverse striai and microscopic re- 

 volving lines ; whorls four, convex ; aperture 

 sub-circular, oblique ; lip simple, acute. 



This species was first found in Cincinnati, 

 0., and described by Mr. Isaac Lea in 

 Trans. Am. Phil. S'oc. ix., 17, 1841. It 

 has since been found in Maine, Massachu- 

 setts, Rhode Island, and New York. It is 

 the smallest land shell in America, perhaps 

 the smallest in the world, its diameter being 

 onl}' four one-hundredths of an inch. 



Mr. E. S. Morse proposed a new genus, 

 Punctum, for this species, in 1864, as the 

 buccal plate ditfers from all other species of 

 Zonites. The jaw of all the others consists 

 of one solid plate, while that of this species 

 consists of sixteen distinct [)ieces. P. min- 

 utissimum is the onl}' species of the genus. 

 Tryon in his Structural and Systematic 

 Conchology, ni., 25, 1884, places it under 

 Zonites as a sub-genus. 



Family Helicidse. An enormous family of 

 land snails containing a great number of gen- 

 era and several thousands of species. The 

 following description, however, applies to 

 all its members. Shell external, usually 

 well developed, and capable of containing 

 the entire animal ; aperture closed by a 

 layer of hardened mucus, (minutely perfo- 

 rated opposite the respiratory orifice) , dur- 

 ing hybernation, which takes place in cold 

 regions in winter, and in hot countries in 

 summer. The principal genus of this fam- 

 ily is called Helix, meaning a coil. The 

 original Helix of Linne included all sorts of 

 land and fresh water shells and has been 

 restricted more and more b}' every author 

 who has written on the subject since his 

 time, until after dropping off genus after 

 genus, making new ones out of the species 

 of the old helix, and even whole new fami- 

 lies, there were still some thousands of 

 species left in 1834, when G-ray separated 

 the genus Nanina. The latest authority, 



after leaving out more than five hundred 

 species of Nanina, and many more of 

 Zonites, gives the number of species of He- 

 lix as thirty-four hundred, which he divides 

 up into forty-seven sub-genera, each with 

 numerous sections or groups. I think the 

 use of the term helix should be abandoned 

 altogether. Many conchologists are in the 

 habit of using the sub-generic names in a 

 generic sense, and even the sectional or 

 group names in the same manner. I pro- 

 pose in these papers, and also in a work on 

 the genera of shells which I am now 

 engaged in writing for publication, to drop 

 the term helix altogether and to use the 

 larger groups, such as Mesodon, Patula, 

 Polygyra, Stenotrema, etc., in a generic 

 sense, and the others as sub-genera. Of the 

 above thirty-four hundred species, only 

 about one hundred and twenty-five inhabit 

 the United States, and only eight are known 

 to inhabit Rhode Island. 



Genus Mesodon Raf., 1831. 



Shell large, sub-globose or orbicularly 

 depressed ; aperture rounded lunar ; peris- 

 tome white lipped, sometimes dentate on 

 the parietal wall, and sometimes on the 

 basal margin, whorls five or six, regular; 

 umbilicus partly or wholl}' covered by the 

 expansion of the lip. Generally of a uni- 

 form pale horn color. 



This genus is found only in the United 

 States. There are twenty species, two of 

 which inhabit Rhode Island. 



85. Mesodon albolabris, Sat. 



This species, the largest in size of any of 

 our Rhode Island land shells, is found 

 everywhere in dark, hard wood forests from 

 Canada to South Carolina, and westward to 

 Nebraska. It is universalh' distributed 

 within the above named limits, and is a 

 very handsome, well proportioned shell. 



It was first noticed by Mr. Thomas Say, 

 the first and greatest naturalist of America, 

 and described by him as Helix albolabris, 

 in the American edition of Nicholson's 

 JBritish Encydopmdia of Arts and, Science 

 published in Philadelphia, 1816, in the fol- 

 lowing words : 



"Shell thin, fragile, convex, imperforated 

 with six volutions, whorls obtusely wrinkled 

 across, and spirally striated, with very fine 

 impressed lines, a little waved by passing 

 over the wrinkles, both becoming extinct 



