No. 531] GUNDLACHIA AND ANCTLUS 



177 



difficult to get any fresh weed except by purchase. I'm 'ing 

 much occupied, I contented myself with having the 

 aquarium filled with Potomac water from the tap. A 

 short time afterward I was surprised to note a large 

 number of young Ancylus with clean translucent shells, 

 on the side of the tank. There had never been any 

 Ancylus in the aquarium except such as might have been 

 put in with Mr. Allen's Anacharis. These had up to 

 February l'l 1 , 11)10, grown rapidly and continued to flour- 

 ish, though the number then visible was only about half 

 that which was noticed in November. In April the 

 Ancylus completely disappeared again. I have not been 

 able to discover where they went to, as the most careful 

 scrutiny of the sparse amount of Anacharis remaining 

 has not revealed any on the stems or leaflets. None of 

 the specimens seemed to have formed any septum and 

 nearly all of them were carrying a small colony of five 

 or six minute hydro-ids on the posterior upper surface 

 of the shell. The shells in February were still too fragile 

 to admit of removal from the glass without crushing, 

 and most of them kept on the side away from the 

 window, on the sill of which the tank stood. They were 

 about 3.0 mm. in length, and remarkably active, moving 

 about on the glass with surprising speed. 



Subsequently Mr. Allen kindly furnished me specimens 

 of all these stages in alcohol ; and I also had the oppor- 

 tunity of seeing some specimens in alcohol which had 

 been sent to Mr. Bryant Walker and Dr. H. A. Pilsbry 

 in 1908, and which were obviously identical with those 

 sent as exam] ties by Mr. Allen to me over a year later, 

 and Dr. Pilsbry thought also with specimens collected 

 at Rock ford, Illinois, in the ancyloid stage. On account 

 of its relations to the Gundlachia it will be referred to 

 here as Ancylus meekiana, since, unless in the Gund- 

 lachia stage, it seems not to have been described. 



Mr. Allen also sent a lot of the wild Ancylus collected 

 in the Thornburg lagoon and which he was disposed to 

 regard as something distinct from his aquarium ancy- 



