198 BOYSIDIA. 



This species differs from B. hunana conspicua by its smaller 

 size, thin lip, more separated angular and parietal lamellae, 

 the presence of a suprapalatal plica, etc. It is less evolved 

 than hunana by the less united angular and parietal lamellae. 



Subgenus BENSONELLA Pilsbry. 



Bensonella PILS., Proc. A. N. S. Phila., 1900, p. 591, foot- 

 note ; type Pupa plicidens. 



The shell is perforate and rimate, conic, minutely granulose, 

 having long, parallel angular and parietal lamellae, and the 

 usual horizontal columellar lamella and palatal plicae, all con- 

 spicuously hooked at their outer ends. Peristome thickened. 



This group is closely related to Paraboysidia, from which 

 it differs conspicuously by having the teeth hooked. It may 

 be regarded as a specialized Paraboysidia. In the sole species 

 known there are many accessory lamellae and plicae. 



Bensonella has several characters elsewhere seen only in the 

 European genus Abida. Such are the interruption of the an- 

 gular lamella (cf. the "spiral lamella" of Abida), and the de- 

 velopment of lamellae between the angular lamella and the 

 suture (as in Abida polyodon}. As Bensonella and Abida do 

 not seem at all nearly related in other respects, these similar 

 structures are apparently homoplastic. The potentiality, 

 rather than the structure itself appears to have been inherited. 

 It may be noted also that some authors have recognized a cer- 

 tain likeness to Odontocyclas. 



5. BOYSIDIA PLICIDENS (Benson). PI. 34, figs. 1-4, 9, 10. 



Shell urnbilicate, ovate-conic, subtrochiform, rather glossy, 

 obscurely striate, corneous. Five convex whorls, the last ven- 

 tricose, ascending in front, tumid at the base. Suture im- 

 pressed. Apex obtuse. Aperture irregular, subtriangular, 

 having 9 folds. Peristome continuous, sinuous, expanded, the 

 margins joined by an expanded callous; right margin im- 

 pressed in the middle outside, thickened and tubercular within. 

 Three parietal lamellae, of which the upper two are long; one 

 dentiform columellar; five palatals, two subbasal being 

 minute. Basal margin having a callous outside. Umbilicus 

 narrow. Length 2, diam. 1% mm. (Benson). 



