PLANORBIS DILATATUS. 23 



impressed suture, upon the right side; and from 

 P. dilatalus, by greater magnitude, wider um- 

 bihc, and oblique aperture. 



Dr. Gould thinks it probable that P. lens is identical 

 with the next species; but the figure and description of it 

 appear to agree niore nearly with P. exacutus; and this 

 opinion is strengthened by the fact that Mr. Lea proposed 

 brongniarticma (instead of lens which was pre-occupied) 

 more than a year after the publication of Dr. Gould's spe- 

 cies, and without making any allusion to the dilatatus of 

 PfeifFer. A less uncouth name than the unlatinized one of 

 M. Brongniart might have been proposed; for as it now 

 stands, it is unpronounceable as a latin word, and the femi- 

 nine form is objectionable, although, in the present instance 

 not as much so as the corresponding masculine term would 

 be. 



PLANORBIS DILATATUS, Gould. 



Plate 4.— Figs. 16—18. 



P. testa minuta, margine carinato; infra anguste umbili- 

 cata; supra subplana, sutura impressa: apertura subovata, 

 et dilatata. 



SYNONYMS AND REFERENCES. 



P. DILATATUS, GouLD. Invert, of Mass., (1841,) p. 210, 

 tiff. 140. 



