THE NAUTILUS. 15 



The examination of this material leads necessarily to a study of 

 the described forms of North American Gundlachia, and the results 

 of this work may properly precede the consideration of the new ma- 

 terial referred to. 



I. 



Gundlachia stimpsoniana Smith. Plate IV. 



This species was described in 1870 (Ann. N. Y. Lye. N. H., IX, 

 p. 399, fig. 6) from specimens collected in ponds at Greensport, 

 Long Island, N. Y., and on Shelter Island. Only the " primary " 

 stage was figured. It has not been found elsewhere, so far as I know. 



Through the kindness of Mr. J. B. Henderson, Jr., I have been 

 able to examine the original lot of this species from the Smith col- 

 lection. It consists of 71 specimens from Greensport and 1 from 

 Shelter Island. 



The Shelter Island example is a young shell that has completed 

 the septum and is similar to the one figured (figs. 10-12). The 

 Greensport set may be divided into four groups : 



1. 60 examples of the primary stage, with the septum in all stages 

 of development, from the first beginnings at the posterior margin to 

 the completed septum. With one exception, these specimens, al- 

 though varying somewhat in size and shape, are similar in all other 

 respects. The matured, or rather, perfected examples, vary from 

 1^ to 2 mm. in length, f to 1 in width and from to | in height. 

 The shape is an elongated oval, the ends bluntly rounded, the an- 

 terior extremity being usually somewhat more expanded. The sides 

 are nearly parallel, usually somewhat constricted in the centre, and 

 rather more so on the right than on the left, but in the smaller spe- 

 cimens are occasionally slightly convex. The apex is blunt, slightly 

 projecting and inclined to the right. It is radiately striate as in 

 Ferrissia. The anterior surface is distinctly ribbed with fine radiat- 

 ing ribs, which, however, do not extend to the apex. The septum 

 for the posterior half or two-thirds is either fiat or, more usually, 

 slightly convex. From about the centre of the shell it is flattened 

 and descends slightly to the aperture. This depression is, no doubt, 

 caused by the body of the animal in moving in and out of the con- 

 stantly decreasing aperture. The lines of growth are curved and 

 delicate, but quite distinct. On completion of its growth the edge 

 of the septum is abruptly turned upwards to the level of the edge of 

 the shell, and the whole margin of the aperture thus formed is slightly 



