250 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



KEY TO THE GENUS ALONELLA. 



I. Eostrum long, bent backwards rostrata, 250 



II. Rostrum short. 



A. Lower posterior angle toothed. 

 a. Shell more or less reticulate. 



* Eeticulated areas minutely striate, pillcliella, 250; excisa, 251 

 ** Reticulated areas smooth. 



t Head depressed exig-ua, 252^ 



ft Head horizontal grisea, 252 



i. Shell marked by lines running diagonally upward and 



backward pyg-iiipea, 25S 



B. Lower posterior angle smooth, shell longitudinally striate. striata, 255 



Alonella rostrata Koch. 



Lynceus roitraitis — Koch, Lilljeborg, Schoedler. 

 Alona rostrata — P. E. Mueller. 

 Pleuroxiis acuih-ostris — Birge. 

 Pleuroxus affinis — Herrick. 



Body long, rapidly narrowed behind; dorsal line strongly arched 

 in front toward the depressed head; the lower margin straight, with 

 0-3 small teeth at the angle. The fornices are broad, but the beak 

 is sharp; the pigment fleck is but little smaller than the eye, to which 

 it is three times nearer than to the beak. The post-abdomen is long^ 

 very much as in A. excisa, but longer. Length 0.4 to 0.5 mm. 

 Schoedler says the lower margin is concave and the angle unarmed, 

 a condition not inconsistent with specific identity, as can be seen in 

 many other species. The shell seems to be variably marked, but most 

 conspicuous are the diagonal, curved strisB. Schoedler compares the 

 sculj)ture to P. exiguus; Kurz, however, leaves the imj)ression that 

 only slight reticulation is present in the female. 



The male has the post abdomen narrowed, ornamented with 

 clusters of hairs behind, and the small claws have no basal spine, 

 while the genital opening is in front of the claws. 



* Alonella pulcliella Herrick. 

 Plate XIII, Figs. 1-3. 



A minute form very recently obtained is described under the above 

 name. Although closely allied to A. exigua, this species is more like 

 Graptoleberis than any other member of the genus. It is the smallest 

 of the Lynceids, excepting A. pygmcea. The shell is high and rather 

 strongly arched; the posterior margin is short and armed with four 

 teeth below, which point in different directions as in Graptoleberis. 

 The head is short and the antennules long. The pigment fleck is o^ 



