62 THE NAUTILUS. 



tion of Bytlunella. To the oue species hitherto known we now 

 add the following : 



Lyogyrus dalli Pilsbry it Beecher, n. sp. 



The shell is umbilicated, smooth, nearly lusterless, of a somewhat 

 transparent horn color. In contour it is globose-turbinate with a 

 short spire and decidedly obtuse apex. The 3 J whorls are quite 

 convex, separated by deep sutures ; last whorl ventricose, being well 

 rounded in every part. The aperture is somewhat oblique, almost 

 circular, its posterior angle being indistinct and obtuse. The peri- 

 stome is continuous and thin, not sinuous, not thickened nor 

 expanded ; but the inner lip is a trifle dilated, and adheres to the 

 body-whorl above the umbilicus; the latter being a deep and rather 

 widely open perforation. 



Alt. 2'6, diam. 2*5 mm. 



The operculum is usually retracted about the quarter of a volu- 

 tion within the mouth ; it is a shining, yellowish, thin and corneous 

 circular disk composed of many close whorls, the nucleus being 

 subcentral. 



The dentition is practically the same as in L. pupokles. The 

 basal denticles are situated higher on the tooth than in Amnicola, 

 and only one on each side is well developed, the outer denticle 

 being more or less obsolete, but rather stronger in L. dalli than in 

 pupoides. 



Locality, Wekiva River, Fla. (C. E. Beecher). 



This species was obtained in considerable numbers by Mr. 

 Beecher in Wekiva River. It may be recognized by its globose 

 contour, resembling the typical Amnicola porata of Say on a small 

 scale ; but it is more globose and has a wider umbilicus than any 

 of our other Amnicolas. Of course a glance at the operculum 

 (which is retained in the shell, as usual in this family), tells one at 

 once that the shell is no Amnicola ; for it is multispiral like the oper- 

 culum of Lyogyrus pupoides Gld., the only species of the genus 

 hitherto known. It will be remembered that Ancey described a 

 Lyogyrus lehnerti some years ago, but this turns out to be a mon- 

 strosity of Amnicola limosa Say. 



This species is named in honor of Dr. W. H. Dall, of the Smith- 

 sonian Institution, who has contributed so largely to our knowledge 

 of the molkisks of Florida. 



Illustrations of shell, operculum and dentition Mill be given in 

 the Monograph of American Amnicolidse, now in preparation by 

 Mr. Beecher and the writer. 



