On the Melanians of Lainarck. 21 



der consideration. Prof. L. will observe that I have attached no 

 uncommon accuracy to my mean results, until the observation at 

 Davenport in Sept. 1839, when I changed ray mode of using the 

 instrument. The observation of 1837 was the second one ever 

 made by me, the instruments had imperfections since remedied, 

 and the probability is, that the compass had accidentally been 

 turned out of the meridian, a thing specially guarded againsi in 

 all subsequent researches. 



Prof. Loomis mentions the " disheartening anomalies" which 

 he meets with in his own researches, and makes some remarks 

 concerning his own observations. He will perceive by the rules 

 which I have prescribed to myself, that I can say nothing upon 

 either of those topics. 



RECAPITULATION. 



1. Prof. Loomis has marked the results of my observations in 

 error, by an assumed hypothesis, admitted to be such, by himself. 



2. He has thought it " implied" that I did not read both ends 

 of the dipping needle, and that the results were therefore not en- 

 titled to so much confidence. This is not true. 



3. He has found a discrepancy in an item of an observation, at 

 Davenport, as published in Vol. xxxix, of this Journal. This 

 turns out to be a typographical error. Prof. L. calculates that 

 the item ought to have been 54. 1 minutes. The item actually 

 was 55 minutes. 



4. He has tabulated the small vacillations in the parts of an 

 observation amounting at most to 8'.75 as "errors of observation." 

 These errors correct each other, and nearly disappear in the mean 

 results. 



Art. in. — Observations on the Melanians of Lamarck; by 

 S. S. Haldeman. 



Lamarck included the genera Melania, Melanopsis, and Pirena, 

 in this family, without having had it in his power to examine the 

 animals. Ferussac unites Pirena to Melanopsis, because he has 

 examined P. atra, Lam. preserved in spirits, and finds that it does 

 not differ from Melanops buccinoidea and costata, which he de- 

 scribed from living individuals. Rang takes the same view, and 

 places Melanopsis between Cerithium and Planaxis. Cuvier ad- 



