670 PROCEEDINGS OF THE ACADEMY OF [DeC, 



tinguishable from Ancylus, may be termed the non-septate form. 

 It is not merely the ancyloid stage grown large, because the young 

 non-septate never has the shape of the ancyloid stage. When of 

 the same length as that, it is a wider shell. This is certainly the 

 case in the Illinois species which I collected about 1886, and, so far 

 as I can make out, in Mr. Allen's Ohio specimens also. It appears, 

 therefore, that in all post-embrj'onic stages the septate form differs 

 from the non-septate. 



It seems certain that the tj^pical forms of Ancylus and the great 

 majorit}' of known species never develop a septate form, which, 

 from Mr. Allen's observations, seems dependent upon physical 

 conditions. Whether Gundlachia is to be retained as a genus depends 

 upon whether we consider the ability to produce the septate form 

 to be a character of taxonomic value. To me it appears to be so, 

 even though the character is not expressed in all individuals or 

 under all conditions. 

 Gundlachia bakeri n. sp. PI. XXVI, figs. 1, 2, 3. 



In the second or septate stage the shell is oblong, the width con- 

 tained twice in the length; sides slightly convex. The obtuse, 

 rounded summit is very close to the posterior end and overhangs 

 the right margin. Back and left slope are strongly convex; posterior 

 and right slopes short and steep. There are a few low, wave-like 

 concentric wrinkles near the embryonic shell and some faint radial 

 lines on the anterior part. The sides curve into the deck, except 

 posteriorly where there is an angle or keel at junction of upper 

 surface and deck. The deck or septum is convex and covers about 

 two-thirds of the lower face. The aperture is oval, its margins 

 elevated, blackish, and a little reflexed. 

 Length 2.8, width 1.4, alt. 1 mm. 



Several dozen specimens were taken during the dry season in an 

 artificial lake or pond in one of the small parks of the city of Para 

 situated between the public market and the Cathedral. Over a 

 hundred specimens of Physa rivalis M. & R., Planorbis anatinus Orb., 

 and what the collector supposed to be Ancylus were taken from the 

 dead leaves and debris in the pond and preserved together in alcohol. 

 Part of the collecting was done by stripping the leaves. On examina- 

 tion of the bottle after arrival in Philadelphia a number of specimens 

 of the septate form of Gundlachia were discovered and the supposed 

 Ancylus is probably the non-septate form, presumably of the same 

 species. 



The pond is two hundred or more feet long, rather narrow and 



