30 



RANDOM NOTES ON NATURAL HISTORY. 



The Shell-Bearing Mollusca of Rhode 

 Island. 



BY HORACE F. CARPENTER. 



Chapter XXVII. 

 8G. Mesodon thyroides, Say. 



This species was also discovered bj' 

 Thomas Sa_y, and described in October. 1817, 

 in the Joxirnal of the Acadeni}/ of Natural 

 Sciences, Philadelphia, as Helix th3-roides. 

 It is the Anchistoma thyroides of H. and A. 

 Adams. The following is the original 

 description by Say: '•'Shell thin, fragile, 

 convex, umbilicate; whorls five, obtusely 

 wrinkled, or rather with equi-distant, grad- 

 ually elevated obtuse lines, and spirall}' 

 striate, with minute impressed lines; lips 

 widely reflected, white and flat before, par- 

 tially concealing the umbilicus; pillar lip 

 furnished with a ver^' oblique tooth. 

 Breadth four-fifths to nine-tenths of an inch." 

 It is found over nearly- the same extent of 

 territory as Mesodon albolabris, but is rare 

 in New England. The only locality where 

 I have been able to find it in Rhode Island, 

 is in the deep woods back of the so-called 

 copperas mine in Cumberland, between 

 Cumberland Hill and Diamond Hill. This 

 species somewhat resembles albolabris, but 

 is distinguished from it by its partly open 

 umbilicus and its oblique white tooth. The 

 outer lip is thinner and more delicate, the 

 aperture is more oblique, and the shell is 

 juore globose, and smaller in size. Western 

 specimens attain a diameter of one inch and 

 the tooth on the inner lip is strong and solid. 

 Rhode Island specimens are never over 

 three quarters of an inch in diameter ; they 

 have a delicate tinge of pink on the reflected 

 outer lip. which is not seen on the solid 

 white lip of the western ones, and the tooth 

 is onl}' slightly developed. Although con- 

 sidered the same as the typical thyroides of 

 Sa}', our shells resemble in general appear- 

 ance the Mesodon bucculenta of Gould 

 more than anj- other American shell. M. 

 bucculenta is southern in distribution and 

 has not been found north of Pennsylvania. 

 I am very much inclined to believe our 

 shells are bucculenta, or rather, that the 

 species called by that name are only local 

 varieties of thyroides. The land shells of 



Rhode Island, compared with the same 

 j species from other parts of the countr}', are 

 I dwarfs. This remark does not apply to the 

 fresh water or marine species, as they are 

 as large and sometimes larger than those 

 found elsewhere. The reason is that our 

 soil, composed mostl}' of granite, is deficient 

 in the lime necessary for the snails to pro- 

 duce exuberant shells. I think if the eggs 

 of our M. thyroides or other species should 

 be taken to Ohio and raised there, the}' 

 would develop Just as large and solid shells 

 as the natives, and vice versa. 



Genus Patula, Held., 1837. 

 " Shell perspectively umbilicated, discoi- 

 dal or turbinated, depressed, rugose or stri- 

 ated ; whorls gradually enlarging ; aperture 

 rounded, unarmed by teeth ; lip simple, 

 sharp." 



This genus is divided into tweut3'-four 

 sub-genera and three hundred and twenty- 

 seven species, distributed all over the world. 

 Three of these sub-genera are represented 

 in Rhode Island, and two more in other 

 parts of New England. 

 87. Patuea (Anguispira) Alterxata, Say. 

 Syns. : 



Helix alternata. Say. 



'• scabra. Lam., Desh., Chem. 

 " infecta, Pfr., Parr., Reeve. 

 " strongyloides, Pfr. Reeve. 

 " mordax, Shutt., Gould, Pfr., Bid. 

 " dubia, Sheppard. 

 Anguispira alternata, Morse, Tryon. 

 This shell, rejoicing in so many appel- 

 lations, was also discovered, and described 

 by Thomas Say in Nicholsoifs Encyclo- 

 jioedia, 1817, as follows: 



" Shell somewhat convex, fuscous, varied 

 or alternating with pale rays ; whorls five, 

 striated across with raised, equi-distant, 

 acute lines, forming grooves between them. 

 Aperture thin and brittle, hp regularh' 

 curved, within glossed with pearlaceous, 

 and when placed before the light the fus- 

 cous lines appear sanguineous. Umbilicus 

 large, exhibiting all the volutions. Three- 

 fourths of an inch wide. Inhabits the 

 Middle States." Since Say's time it has 

 been found in ever}' state east of the Rocky 

 Mountains. 



Morse's description of the New England 

 specimens in the American Naturalist, 

 June, 18G 7, differs somewhat from Say's: 

 ".Shell flattened, heavil}^ striate, light horn 



