THE NAUTILUS. 8.3 



anterior slope only slightly convex, seem to be also referable to this 

 species. 



Distinguished primarily by its small size, this spec'ies is well char- 

 acterized by the prominent, obtuse apex, the short, straight posterior 

 slope and long, convex anterior slope. It is very close in general 

 appearance to A. s/tiniekii, but seems to differ persistently in having 

 the apex, which is less excentric in position, projecting decidedly 

 .upwards and not depressed at the tip as in that species, the anterior 

 slopes not quite so convex, while the posterior slope is longer, more 

 oblique and nearly straight. The extreme lateral compression char- 

 acteristic of shimekii is not present in this species, the right slope 

 being nearly straight ; this difference is particularly marked in the 

 immature shells, which in shimekii are decidedly narrow and pro- 

 portionately higher than the mature shell, while in pumilus the pro- 

 portions are nearly the same. Sterki's types are immature examples, 

 to which his statement, that ' the sides are parallel," is quite appli- 

 cable, but in mature examples the lateral margins expand a little and 

 become more curved as shown in the figure, which is from one of the 

 largest specimens seen, the dimensions being : 



Length 2.75, breadth 1.75, alt. 1.0 in. in. 



EXPLANATION OF PLATES. 



All the figures on each plate are drawn on the same scale, but 

 those on Plate VI are somewhat more enlarged than those on Plate V. 



PLATE V. 



Figs. 1-3, A. parallelns Hald. Little Lakes, N. Y. 

 Figs. 4-6, A.parallelns Hald. Pine River, Marquette Co., Mich. 

 Fijrs. 7-9, A.parallelus Hald. Caribou, Me. 

 Figs. 1012, A. elatfor Hald. Kentucky. 



PLATE VI. 



Figs. 1-3, A. filt>i>us Con. Coosa River, Ala. 

 Figs. 4-6, A. filosus Con. Coosa River, Ala. 

 Figs. 7-8, A. filosus Con. Cahawba River. Ala. 

 Figs. 9-10, A- haldemani Bgt. Holston River, Washington Co., 

 Va. 



Figs. 11-13, A. haldemani Bgt. Doe River, Tenn. 

 Figs. 14-16, A. b/irealls Mse. St. John's River, Me. 

 Figs. 17-19, A. shimekii Pils. Headman's Run, Neb. 

 Figs. 20-22, A. pumilus Sterki. Tuscawaras River, O. 



