1851.] 277 



October 2Ut. 



Vice-President Bridges in the Chair. 



Mr. Lea read a paper on the genus Acoatma of D'Orbigny, a new 

 fresh water molkisc of the order Dhni/aria, from the river Guadua, 

 New Granada. 



Mr. Lea considers this shell as one of the most remarkable and interesting 

 which has ever come under his notice. The fact that it is in its young state a 

 free limusculose shell, and in its mature state an affixed ttniimtsculose shell, 

 places it among the anomalies which zoologists find it diffiult to understand, but 

 which, in this case, points out its true position in a natural arrangement. Mr. 

 Lea expressed his convictions that this shell, now so well described by M. 

 D'Orbigny, belonged to the same genus which Ferussac described in 1823, in the 

 Mem. of the Soc. Nat. Hist., Vol. 1, under the name of Mulleria, if it be not of 

 the same species, a single specimen (adult) of which had then only been seen. 

 Ferussac, considering the general resemblance of Mulleria to Ostrea, thought it 

 ought to be put alongside of, if not in, the latter genus. Brongniart and Latreille 

 thought it ought to go between Spo?idi/lics and Area. Other authors had assigned 

 it to various positions, while some doubted whether it was anything more than a 

 malformation. The perfect specimen, in its junior and adult state, if it be 

 Mulleria, now banish all difficulties. Mr. Lea thinks now, in placing Mulleria 

 (Acostaea) in its true position, at the head of the order Monomyaria, where it 

 makes the link with Diviyaria, it forms an easy transition from the first to the 

 second order. Thus retaining the trace of one while it passes so curiously into 

 the other. Nihil 2>er saltum, 



Mr. Lea, under the impression that D'Orbigny's Acostaa Guaduasana may 

 prove to be a distinct species from the shell described by Ferussac, under the 

 generic name of Mulleria, while it may belong to the same genus, proposes to 

 give the name of that distinguished zoologist to it. That of Guaduasana should be 

 retained of course for D'Orbigny's species. The genus would then represent 

 Mulleria Fertcssacii, and Mulleria Guaduasana. 



The paper being intended for publication in the Journal, was re- 

 ferred to Dr. Leidy, Dr. Ruschenberger, and Dr. Wilson. 



Dr. Fisher, on behalf of the Committee on the Memoir of Dr. 

 Morton, reported that they had selected the Hall of the University of 

 Pennsylvania, and had appointed the first Thursday in November as 

 the time for hearing the Memoir read by Dr. Meigs, provided the con- 

 sent of the Trustees of the University could be had, notice of which 

 would be given. 



On motion of Dr. Leidy, it was 



Resolvtd, That persons, not members of the Academy, vii\o may 

 contribute to the Museum or Library specimens of Natural History or 

 Books, deemed of sufficient value by the Curators or Librarian, be en- 

 titled to a ticket of admission to the Museum on public days, for a 

 period of six months. 



