ACADEMY OF SCIENCES. 175 



33 Planorbis subcrenatus Cpj-., common, 

 I found the same species there in 1862. 



34 Pomatiopsis intermedia Tryon. Having recently found a 

 colony of this species near the city, I have observed the following habits, addi. 

 tional to what Stimpson gives of the types. Many specimens I found in the 

 water, but close to the surface, on cresses, etc., were accompanied by eggs (May 

 6tb) enclosed in capsules like those figured by Stimpson as of Amnicola porata 

 and adhering to plants. Most of the specimens, however, lived on a sloping 

 bank, constantly moistened by spring water, shaded by a dense growth of herb- 

 age and bushes. These had no eggs with 'them, and, as they were much larger 

 and more robust than those in the water lower down, I supposed these to be the 

 different sexes. As no other species of this family occurred in the stream, there 

 could be no mistake about the eggs found. They lived in a damp glass for 

 over a month. On a careful comparison of the animals of the two former un- 

 der the microscope, I found that those in the water were of the same species, 

 but that they were of both sexes, and that the difference in shells was caused by 

 their being encased with black oxide of iron, by which growth was retarded 

 and the whorls often forced to form a loose spiral, especially near the mouth, 

 as in the so-called " Valvata pupcndea " Gould. I have also received this form 

 from Santa Cruz and other localities, and formerly thought it was a distinct 

 species. The animal is iuky black above, foot white beneath, and a large ivhite 

 patch around eyes. The encrusted ones merely show the colors less distinctly. 

 The form agrees with that of P. lojndaria. Mr. Binney's figure of" Jmnicola," 

 p. 81, also represents the under surface of this genus, as he refers the species 

 to this genus on p. 94. 



Professor Bolaiider read a communication from Professor Asa 

 Gray, of Cambridge, inquiring about the intended invitation of this 

 Academy to the American Association for the Advancement ot 

 Science. Dr. Cooper stated that an invitation had been extended ; 

 but to set all doubts at rest, it was unanimously resolved that the 

 American Association for the Advancement of Science be again in- 

 vited, by this Academy, to hold their annual session for 1872 in 

 the city of San Francisco. 



Mr. H. Heynemann advised the propriety of requesting the 

 Chamber of Commerce and other bodies of the city to unite with 

 the Academy in the invitation ; and it was resolved that this ques- 

 tion be discussed at the next meeting. 



On motion, Mr. Elisha Brooks was appointed to bring the action 

 of the Society before the Board of Trustees of the Academy, and 

 urge immediate action in the matter. 



