1913.] NATURAL SCIENCES OF PHILADELPHIA. 671 



winding, and averages three or four feet deep. It empties by an 

 overflow and is supplied by a small fountain which was always 

 playing on the numerous occasions when the park was visited. 

 The large amount of dead leaves and debris on the bottom of the 

 pond makes it probable that it has not been drained for a long time, 

 if ever, since its construction. 



This species, named for Dr. Fred Baker, who collected the series, 

 differs from the form figured by Nordenskiold by its smaller size 

 and the far more eccentric apex. The position of the apex will also 

 serve to separate G. bakeri from G. textilina Guppy of Trinidad 

 and all other known species of the genus. A large series taken is 

 very constant in size and form. Specimens in the first or Ancyloid 

 stage and others with the septum in various degrees of development 

 occurred in the same gathering. There were none, however, in the 

 third or complete Gundlachia stage. 



With the Gundlachia just described there were many specimens of 

 an Ancyloid which may be the dimorphic form alluded to above, in 

 which the septate stage is omitted, or possibly it inaj^ be a distinct 

 species of true Ancylus.'^ These shells (PI. XXVI, figs. 4 to 8) are thin, 

 fragile, corneous, and diaphanous, oval, the apex slightly behind the 

 posterior fourth of the length and almost overhanging the right 

 margin; anterior and left slopes convex, posterior and right slopes 

 more or less concave; apex rounded, with a slight apical depression, 

 the embryonic shell minutely pitted; surface elsewhere marked 

 with faint growth lines and minute, unequal radial striae, wanting 

 on the short slope below the apex. 



Length 4.1, width 3, height 1 mm. 



With some resemblance to A. excentricus Morelet, this form differs 

 by its broader contour and more eccentric apex. 



The young shell, 2.4 mm. long (PL XXVI, fig 4), is much wider than 

 the ancyloid stage of G. bakeri of similar length, the breadth con- 

 tained only about 1.4 times in the length, while an Ancyloid of the 

 same length is twice as long as broad. 



Whether this form will turn out to be the non-septate form of 

 G. bakeri or a distinct species of Ancylus is an open question, but 

 I incline to the former view. 



6 The South American Ancyli do not belong to any of the subgenera estab- 

 lished for northern species. In most of them the embryonic shell is punctate, 

 pitted, or pock-marked and of an obtuse, rounded shape, with the usual apical 

 depression. This group may be called Hebetancyliis, type A. moricandi Orb. 

 Others have an acute, hooked apex, also shghtly punctate near the margin of 

 the embryonic shell, subgenus Uncancylus, type A. barilensis Moricand. Both 

 groups are sinistral. 



