51 



Remarks on the weight op the shells of certain species ot 

 CoLiMACEA. By C. B. Adams Nov. 1849. 



The average weight of the full grgwn shells of a given species of 

 the Mollnsca is an interesting item in its history. The ratio between 

 their size and weight varies so much in diiferent species, that the 

 usual precise statements of the former convey no information of any 

 value respecting the latter character. We give therefore a few ex- 

 amples, which ii.dude the most minute terrestrial species that exist in 

 the collection of Amherst College, and which are probably among the 

 most minute that have been hitherto discovered. Several specimens 

 were weighed together, both for the purpose of dividing any error in 

 the process, and of obtaining an average result. Using the balance 

 of analytical chemistry, and taking ten or more individuals of the 

 minute species, we obtain quite exact results. The principal 

 sources of error in the comparison of species arise from the dilFer- 

 ence in the mode of preservation of the shells. In the veiy small 

 species, the animals are usually dried up in the shells; but if not taken 

 alive, they may have lost more or less of the solid matter in the ani- 

 mal. But the difference of weight resulting from this cause cannot 

 be considerable as compared with the entire weight of the shell, for the 

 total solid matter in the soft parts is small. In many operculated 

 species, the operculum is unknown, and we have therefore excluded 

 this part in all the examples of such species. 



In the following table, the fir?t column of figures contains the num- 

 ber of specimens which were weighed together, and the second column 

 —their aggregate weight, and the third — their average weight, in 

 decimal parts of a grain. 



1. Cyclostoma avena Ad. Jamaica. 20 4.025 .2012 



0. " haemastoma Moric. 

 10. " Jaraaicensis ' Sowb. 



