78 



RANDOM NOTES ON NATURAL HISTORY. 



The Shell-Bearing Mollusca of Rhode 

 Island. 



BY HORACE F. CARPENTER. 



Chapter XXXIII. 

 120. Melampus Bidentatus, Say. 



Syns. : 



Melampus biplicatus, Pfr. 



Auricula biplicata, Desh. 



Auricula cornea, Desh. 



Auricula bidentata, Gld., DeKa}', Kuster, 



Melampus bidentatus, Say, Russell, Pfr., 

 W. G. Binney, etc. 



Shell ovate-conic ; whorls five, the body 

 whorl three-fourths the length of the shell ; 

 the others are flattened, forming a short 

 blunt spire ; suture distinct ; aperture long 

 and narrow ; outer lip thin and sharp ; inner 

 lip furnished with two folds or teeth ; with- 

 in the outer lip are seen several ridges which 

 do not reach to the margin. Length one- 

 half inch by three-tenths in breadth. 



It inhabits marshes on grass just below 

 high tide. It crawls up the stems of the 

 grass to escape the rising tide, but can bear 

 submergence in salt water without injurj^. 

 It is ver}^ common in Rhode Island though 

 extremely' rare north of Massachusetts Ba}'. 

 It is found everjwhere near Narragansett 

 Bay and along the ocean shore as far south 

 as Florida. 



The young shells are usually smooth and 

 dark brown, ornamented with two or three 

 revolving bands. As they grow older they 

 become eroded and the surface becomes 

 rough and of a greyish v^hite color. The 

 ridges within the outer lip are not developed 

 until the shell is fulh' matured so that it is 

 rare to find a perfect specimen, i. e., having 

 the ridges and bands with the smooth sur- 

 face and brown color united in one individual. 



Family Otinidse, not represented in 

 America. 



Family' Limnaiidae. 



The members of this large group of mol- 

 lusks inhabit fresh water rivers, ponds, and 

 ditches in all parts of the world and it is 

 almost impossible to find any body of water, 

 however small, which does not contain one 

 or more species of this familj'. While on a 

 visit to German\^ this spring, I noticed in a 



small town, ditches of stagnant water stand- 

 ing in front of some of the houses, not over 

 three feet in witdh, and from two or three 

 inches to two feet in depth, evidenth' recep- 

 tacles for the sewage of the adjoining 

 houses, yet in these ditches were living thou- 

 sands of specimens of at least seven difl^erent 

 species of this family. 



These animals although living in water 

 are air breathers like all of the Pulmonata 

 and thei'efore the}' are obliged to come often 

 to the surface to obtain air. They float 

 along on the water, with the foot or creep- 

 ing disc just level with the surface, and the 

 shell hanging down beneath. By expel- 

 ling a portion of the air contained in the 

 lungs they can immediately sink to the bot- 

 tom. The}- lay their eggs in spring and 

 early summer on stones and sticks in clus- 

 ters surrounded b}' a gelatinous substance. 

 Under the microscope we can watch day by 

 day the development of the eggs and final- 

 1}' the little mollusks eating their way out of 

 the jelly with which they are surrounded, 

 and provided even at this time with a minute 

 shell. Like the terrestrial mollusca, both 

 sexes are united in each individual. - All 

 the air-breathing, fluviatile mollusca belong 

 to this one family which is divided into four 

 sub-families, three of which are represented 

 in Rhode Island. 



Sub-family Limnieinffi, with twelve gen- 

 era is represented in Rhode Island by three 

 genera and eight species. 



121. LiMN.EA (Radix) Columella, Say. 



Shell thin, fragile, horn colored ; whorls 

 four, longitudinally wrinkled ; spire promi- 

 nent, acute ; suture not much impressed : 

 aperture ovate, dilated. Mr. W. G. Binney 

 in Fresh Water i!Shells of North America^ 

 1865, has included (as synonymes) a dozen 

 or more shells described by different authors 

 at different times ; some of these are un- 

 doubtedl}' distinct species of themselves. 

 There is one variety, differing much from 

 the typical species, which was originall}' de- 

 scribed as new, and in m}' opinion ought to 

 be considered as a separate species. The 

 author, however, afterwards seemed disposed 

 to regard it as a strongly marked local varie 

 t}' of columella, because it had never been 

 found in an}' other place than the muddy 

 pool in Cambridge where he first discovered 

 it, and other writers since have taken his 

 later view of the subject. This species I 



