150 LAND AND FRESH- WATER SHELLS OF N. A. [rART IL 



From one of the same lot the lingual membrane fifrured on page 

 148 was drawn. 



Gundlacliia meeliiana, Stimpson. — The full-grown shell, in 

 general form, is ovate. It is much broader than in G. ancylifortnis, and 

 has a less ovate aperture than in G. californica, as may be seen hy com- 

 parison of the figures. The shell consists of two distinct parts, and from 



above looks very much like a small 

 Fiff. 252. '^^^ thick, black Ancylns, sticking 



obliquely and to the right upon the 

 posterior end of the back of a larger 

 thin and whitish one. These two 

 parts we will call, for convenience, 

 respectively the smaller shell and 

 Gundlnchia meekiana. the larger shell. The two parts nearly 



resemble each other in outline, each 

 being oblong, roundedly truncate before, and narrowed and somewhat 

 obliquely truncated behind, the right posterior angle being prominent. 

 The dorsal part, or smaller shell, as before stated, is black opaque, and 

 comparatively thick. It is about one-third as long as the larger shell, and 

 has the usual form of a young Ancylus, the very obtuse apex being at the 

 posterior third ^ its length and inclined to the right. Anteriorly it is 

 continuous with the dorsum of the larger shell, but posteriorly it projects 

 freely over and beyond the margin of that shell, at its posterior dexter 

 angle, at a distance equalling rather less than a fourth of its own length. 

 Inferiorly, the entrance of this projecting portion of the smaller shell is 

 closed by a flat septum, extending from margin to margin, and continuous 

 anteriorly with the dorsum and internal shelf of the larger shell presently 

 to be described. 



The large* shell is thin, translucent, presenting signs of rapid growth, 

 and usually of a whitish or very pale horn-color. It is more expanded to 

 the left than to the right, the dorsum and left slope being strongly convex, 

 while the right slope is nearly straight. It is marked with prominent 

 strise of growth and indistinct radiating lines. Within, at the narrower 

 posterior end, there is a rather strong white shelf, formed hy the soldering 

 of the dorsum of the larger to the septum of the smaller shell, which ex- 

 tends forward and upward, nearly to the bottom of the concavity, leaving, 

 however, an aperture which leads into the cavity of the smaller shell, in 

 which the liver of the animal is seated. This aperture is exactly semi- 

 lunar in shape, its longer diameter being of course coincident with the 

 width of the smaller shell and equalling about one-third that of the larger 

 shell. In younger specimens the shelf is a little less extensive, and the 

 apical aperture somewhat larger. 



The soft parts of the animal, except in the form of the visceral sack, 

 agree so closely with those of true Ancijli, that I have not succeeded in 

 finding any differences of importance. I add here a figure of its lingiial 



