1888.] natural sciences of philadelphia. 121 



March 6. 

 Mr. Thomas Meehan, Vice-President, in the chair. 



Twenty-nine persons present. 



Action of Hydrofluoric Acid on a Sphere of Quartz. — Dr. Otto 

 Meyer reported an experiment, which he had undertaken in con- 

 nection with Mr. Sam'l. L. Penfield. A sphere of quartz was sub- 

 jected to the action of hydrofluoric acid for more than two months. 

 The acid dissolved the quartz, princii^ally in the direction of the 

 main axis and thus flattened the sphere. In the direction of the 

 lateral axes the etching action proceeded with much less activity and 

 at three places on the periphery the acid had not eaten away any of 

 the material, but left the original surface of the sphere intact. These 

 three places were situated at one end of each of the lateral axes, the 

 result being a triangular disc. This experiment shows that a mineral 

 may be soluble in a liquid in certain directions and on certain planes 

 while at the same time insoluble in other directions and on other 

 planes. Dr. Meyer exhibited the result, the object resembling a 

 three cornered lens. — A more detailed account will be given else- 

 where. 



Remarks on the Phylogeny of the Lamellihranchiata. — Dr. Ben- 

 jamin Sharp brought forward some points regarding the classifica- 

 tion of the Lamellihranchiata, and stated that in considering this 

 group, a diversity of type was to be found that is equal to, if not 

 greater than that found in any class of the animal kingdom, with 

 the possible exception of the Hexipoda. 



In examining the different forms, he pointed out two well marked 

 extremes, Ostrea and Aspergillum. In the former as is well known, 

 the two large unequal shells entirely cover the body, and they are 

 closed by one large muscle, the adductor. The large and important 

 organ, so common in the Lamellihranchiata generally, the foot, is 

 entirely absent. The mantle edges are separated for nearly their 

 whole extent, and there is no indication whatever of the mantle 

 uniting to form a siphon. 



In Aspergillum, on the other hand, the two shells are so diminu- 

 tive, that they only cover an exceedingly small area of the animal's 

 body, the siphon is enormously developed, and it is protected by a 

 secretion of carbonate of lime, in which the shells are immovably 

 embedded; the mantle is closed throughout its entire length, except 

 at the anterior end, where there is a minute opening, and at the 

 mouths of the two siphonal tubes. 



His object in making the communication was to prove that these 

 two very marked and different types of Lamellihranchiata arose 

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