ENTOMOSTE.ACA OF MINNESOTA. 241 



pressure, but there is nevertheless greater proportioual length than 

 in ordinary specimens of A. quadrangidaris, and we may have to do 

 with a new species. 



Accordingly we quote our original description. 



"Form sub-quadrangular; height about once and one-half in length; 

 the dorsal outline forming a regular and low curve from end of head 

 to upper posterior margin; lower outline very slightlj^ sinuate, ante- 

 rior one not at all; posterior angles rounded; head nearly horizontal; 

 eye of moderate size; pigment fleck considerably smaller; antennules 

 rather large, with unequal sensory hairs at the end, one spine just 

 above the end in front and a bunch of minute hairs near the base 

 behind; antennai comparatively large, basal joint spiny, outer ramus 

 with three sette, two of which have thorns at their middle, also a termi- 

 nal spine; inner branch with two of the terminal setse thorned and the 

 upper lateral sette reduced. The post-abdomen is very broad and 

 short, expanded below and rounded at the end; the terminal claws 

 are straightish, denticulate, and the spine at the base is also dentate; 

 there is a series of heavy spines on the upper margin of the post-ab- 

 domen, accompanied by a series of scales on the side. The shell is 

 unornamented and fringed below with short bristles. Length 0.9 mm., 

 or more. This fine species is recognized by its smooth shell, the hori- 

 zontal position of the head, and the form of the post-abdomen; it be- 

 longs among the largest of the genus. Lakes near Minneapolis not 

 rare. 



"Birge quotes A. spinifera from Wisconsin. In all probability that 

 species is the younger stage of the above." 



The American form, which we identified with Alotia uhlon[/a, was 

 said to differ from A. quadranguJaris in the following points: 



"The greatest height of the shell is anterior to the middle; the 

 lines are less evident, and all confined to the lower part of the shell, 

 while the centre of the valves is marked with very minute striae; the 

 pigment fleck equals the eye, and the post-abdomen is of about the 

 same width throughout and hardly as round below. This and the 

 preceding species have a well-marked keel on the process of the labrum. 

 The size is greater, this being one of the largest and most abundant, 

 as well as one of the most striking species. It, perhaps, should rank 

 as a well-marked and permanent variety of the above. Length 0.9 to 

 1.0 mm. The abdomen of the male is narrowed at the end and lacks 

 the teeth. Lakes about Minneapolis. 



"(A small form of A. quddrattgularis in Lake Calhoun had the eye 

 and pigment fleck equal and the terminal claw smooth.)" 



We are satisfied that a wide range of variation must be allowed 

 for. The presence or absence of markings is unreliable. 



