CHIEFLY OF THE UNITED STATES. 15T 



Remarlcs. — Among a number of fine fresh-water and land shells which I owe to 

 the kindness of Dr. Trask, were four specimens of this heretofore undescribed species. 

 la the general form of the shell there is a resemblance to Ampullaria neriioides, 

 D'Orb. In the form of the columella it resembles the genera Littorina and Anculosa, 

 but the outer lip is very effuse and totally without any thickening or reflexion. The 

 columella is indented, and has at each end a maculation of brown, which is the case 

 with some of the Anculosce. It is a very thin shell, and quite diaphanous. The 

 spire is but very little raised above the plane of the whorls, and the apex in each of 

 the specimens is slightly worn off. 



Planorbis Traskii. PL 23, fig. 70. 



Testa magna, tenebroso-cornea, subcylindracea, minute, orebre et regulariter striata, superne late et pro- 

 fundite depressa, inferne magis excavata; anfractibus quinis, superne acute carinata ad periphariam, 

 inferne obtuse carinata ; apertura auricuteformis. 



Shell large, dark horn-color, nearly cylindrical, minutely, thickly and regularly 

 striate, above widely and deeply umbilicate, below largely excavated ; whorls five, 

 above acutely carinate near the periphery, below obtusely carinate ; aperture e.ar- 

 shaped. 



Proc. Acad. Nat. Sci., 1856, p. 80. 



Hab. — Hern Lake, Tulare County, California, Dr. Trask. 



My cabinet and cabinet of Dr. Trask. 

 Diam. 1-5, Length -86 inch. 



Remarlcs. — This is certainly the most remarkable species of Planorbis yet observed 

 in the United States. It approaches in general form to corjndentus, Say, but is a 

 much larger species, having very much smaller strias. The depressions above and 

 below are also much greater, and the superior carina is more acute. The striee of 

 the true corpulentvs are coarser than I have observed in any other American species, 

 while in this species they are among the finest and closest of the various species. 



The form of Traskii is very remarkable in being high for the width, being really 

 barrel-shaped. I should call this shell sinistral, but Mr. Say calls the corimlentus, 

 which opens on the same side, dextral. Mr. Haldeman calls the spiral side the left 

 side, owing to its position in the animal. A single specimen only was received from 

 Dr. Trask, and this unfortunately having lost part of the lip, renders it impossible to 

 say what might be the form of that important portion. I doubt very much its being 

 very effuse. I name this fine species after Dr. Trask, who has kindly furnished me 

 with all the species described above from California, on pages 154 and 157. 



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