On the Melanians of Lamarck. 21 
der consideration. Prof. Li. will observe that I have attached no 
uncommon accuracy to my mean results, until the observation at 
Davenport i in Sept. 1839, when I changed my 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 against 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 res observations in 
error, by an assumed hypothesis, admitted to be such, 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 Faaghes in an item of aieitbesr totic ot 
ed in Vol. is bi Journal. This 
oe caleulat ee 
Davenport, as 
turns out to be pogra 
the item ought to ave been BAL Sino 
was 55 minutes. sn e 
4. He has tabulated the small vacillations in ie vai of an 
observation amounting at most to 8’.75 as “errors of observation.” 
These errors correct each other, and iti hecahiie im ag mean 
results, é 
y ried 
oe 
Arr. II.—Observations on the Melanians of aged by 
. HaLpeman. 
Lamarck included the genera Melania, Melanopsis, and Pirena, 
in this family, without having had it in his power to examine the 
animals. F'érussac 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- 
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