Puhnonifera of Jfaine. 



Fig. 54. Fig. 58. 



23 



Fig. 55. Fig., 59. 



Figures 54 and 55 represent a specimen of Vallonia minuta 

 from Portland, Maine, Figures 58 and 59 represent a specimen 

 of Vallonia pulchella from Tuscany. The principal points of 

 difference will be seen in the more depressed fonn of V. minuta 

 as compared with V. pulchella, the whorls are not as large, the 

 labrum as it joins the labium near the umbilicus is more directly 

 under the body whorl than in V. pulchella ; the upper part of the 

 aperture is not so arching as in the European shell, and the entire 

 aperture, modified by these differences, is not so completely cir- 

 cular as in V. pulchella, while the lower portion of the last whorl 

 in the European shell is slightly flattened ; in V. minuta the 

 outline forms a perfect curve. The principal points of difference 

 between the two species is seen in the angle formed by the 

 dotted lines in Figures 55 and 59, one of which passes through the 

 axis of the shell, and the other parallel with the plane of the 

 aperture ; the line perpendicular to the axis of the shell in rela- 

 tion to the plane of the aperture, forms a greater angle in V. 

 pulchella. This we consider a very marked and important dis- 

 tinction between the tAvo species. V. minuta is generally more 

 translucent ; the periostraca of the two shells when highly magni- 

 fied exhibit slight differences also. 



W. Thomson of England gives the dentition of V. pulchella 

 thus, number of rows 65, number of plates in a row 30, total, 

 1950. We find V. minuta to stand thus, number of rows 73, 

 number of plates in a row 23, total, 1679. 



