96 



RANDOM NOTES ON NATURAL HISTORY. 



Sub-family Planorbinffi. 



The shells of this sub-famih' are all dis- 

 coidal, spiral, and the apex sunk in the nu- 

 cleus of the coil; whorls three to seven, 

 smooth or striate, sometimes keeled. 



The animals have the orifices of their gen- 

 erative, excretory and respiratory organs on 

 the left side like those of Physa, but their 

 shells are dextral like all other gasteropods, 

 with few exceptions. This sub-family con- 

 tains two genera, Planorbisand Segmentina, 

 both of which are represented in Rhode 

 Island. 



Genus Planorbis Guettard. 



All the shells of this genus existing in the 

 Old World, belong to one type and number 

 only about thirt}' species, eleven of which in- 

 habit Great Britain and the remainder scat- 

 tered through Pkirope, Africa, India, Ceylon, 

 and Australia. On the other hand we have 

 over seventy species in America, belonging 

 to five or six distinct types or sub-genera. 

 The\- are all ver}- sluggish in their habits and 

 prefer stagnant pools. 



129. Planorbis Lentus, Say. 



Mr. Sa}' discovered a shell in a canal near 

 New Orleans and afterwards other speci- 

 mens of the same in Mexico, which he de- 

 scribed in 1834 in the American Conchol- 

 ogy, published at New Harmony, Ind., un- 

 der the name of Planorbis lentus ; previous 

 to this, in 1817, he described a shell which 

 he called Planorbis trivolvis. Authorities 

 quote both species from all parts of the 

 United States, but the subject is somewhat 

 mixed. I have never found or heard of P. 

 trivolvis being found in Rhode Island, but 

 haveplentj'of P. lentus, if one can tell any- 

 thing by descriptions and plates. Professor 

 Adams in speaking of this shell refers it to 

 P. trivolvis in the Shells oj Vermont, and 



in his list of " Middlebury shells ' to P. cor- 



pulentus. Gould says : " This shell has 



hitherto borne the name 



New England, but it is 



of Say, and is either his 



species.' Gould's figure 



of lentus is referred by 



of trivolvis in 

 not the trivolvis 

 lentus or a new 



and description 

 Hadleman to P. 



fallox. W. G. Binney says : " It is not the 

 lentus of Say," and lefers it to trivolvis. Per- 

 haps trivolvis and lentus are the same spe- 

 cies, modified b^' localij', etc. But I am of 

 the opinion that our Rhode Island lentus is 



a distinct species from the trivolvis of tiie 

 Middle and Western States. 



It is a discoidal shell, concave on both 

 sides, the spire sunken in on the upper side 

 showing three volutions, just like the umbili- 

 cus on the under sides of many helices ; 

 lower surface cup-shaped, formed of four 

 whorls ; aperture large ; lip sharp, thickened 

 within by a dark reddish-brown callous ; color 

 of the shell brownish or chestnut ; diameter 

 seven-tenths of an inch. 



My specimens were found in a meadow 

 overflowed with water near Ashton, on the 

 Cumberland Hill road. What seems strange 

 in the instincts of these animals is, that 

 although the place overflowed is quite large, 

 and after searching in vain, by wading into 

 it in several places, and in looking carefull_y 

 around its entire curcumference, not a shell 

 could be found ; they were found abundantly 

 in one spot, exactly under the shadow of a 

 willow tree, standing at the edge of the pond 

 near the road. Other species of shells were 

 found in all parts of the pond, but of this 

 species none, excepting those under the tree. 



130. Planorbis (Helisoma) Bicarinatus, 

 Say. 



Syns. : 



Helix angulata, Rackett, Wood, Hanlej'. 



Helix bicarinatus, Eaton. 



Planorbis engonatus, Conrad, Lister. 



The sub-generic name, Helisoma, was 

 given by Swainson in 1840, to those species 

 of Planorbis which are ventricose in form, 

 with but few whorls, and in which the spire 

 is sunken below the body whorl. This sub- 

 genus includes eight species of North Amer- 

 ican Planorbis, only one of which, bicarina- 

 tus, inhabits Rhode Island. 



The shell is orbicular, deeply excavated and 

 carinated on both sides, color brownish 

 yellow ; spire sunken, forming a cavit}' 

 nearly as deep as that on the under side ; 

 whoris three and a half, visible on both 

 sides ; aperture large, embracing a large 

 part of the body whorl and vaulted above ; 

 lip white and expanded, interior brownish 

 red ; diameter of shell one-half inch. It 

 ranges from New England to Kansas, and 

 from British America to Georgia. It is not 

 very common in Rhode Island, but is found 

 in still water, on the margins of large ponds 

 and not in muddy pools. It is quite abun- 

 dant in the Providence and Worcester 



