STATE GEOLOGIST. 87 



The front margin is strongly convex. The post-abdomen is long 

 and slender, resembling that of Camptocercus, and is notched at 

 the distal extremity; it has two rows of fine teeth and some fine 

 scales above them. The terminal claws are long, slender, with a 

 basal spine, a spine in the middle, and are serrated. The antennules 

 are long and slender, but do not reach to the end of the rostrum. 

 They have each a flagellum and sense hairs. The antennae are 

 small and have eight (su) setae and two (iot) spines. The labrum 

 resembles that of A. leucocephalus, but is slightly prolonged at the 

 apex. The intestine, caecum and color resemble those of Acrope- 

 rus. There is a trace of a keel present on the back." 



The specimens seen in Minnesota resemble this species very 

 nearly, apparently, but there are some differences. The terminal 

 claw of the post-abdomen has an increasing series of spines to the 

 middle; there seems to be no lateral row of scales beside the anal 

 teeth; the abdomen is rather broad at the base and narrows toward 

 the end. The shell is not square behind. The lower margin has a 

 few long hairs anteriorly which are followed by a series of teeth, 

 and in the concave part a somewhat longer set to a point just be- 

 fore the lower curved angle. 



The pigment fleck is nearly or quite as large as the eye. The 

 antennule is shorter than the beak (which is almost as in Pleuroxus 

 hastatus), and has a flagellum about midway; at its base it is nar- 

 rowed and inserted on a prominence. 



The embryo still in the brood sac had a more elongate form and 

 hexagonal reticulations upon the shell, while the antennules were 

 longer than the very long beak, and the pigment fleck was smaller 

 than the eye. Length of female 0.52 mm. The color is darker, 

 and the striae more numerous, than in A. latissima. 



Series B. 



This section includes forms with (usually) no keel above, or, if 

 keeled, the post-abdomen is not long. The majority are highly 

 arched dorsally, and have comparatively short post-abdomen and 

 pointed beak. The antennae are usually feeble and the motion slow. 



A. Post-abdomen nearly round in outline, armed with very long stout spines, terminal 

 claw with one minute basal spine or none ; greatest hight of shell about equal to 

 the posterior margin. 



1. Genus Leydigia. 



B. Greatest hight of shell moderately exceeding that of posterior margin ; post-abdo- 

 men more or less triangular, armed with bristles ; shell marked with hexagonal 

 meshes. 



(a) Head nearly horizontal, blunt ; post-abdomen prominent in the anal region. 



2. Genus Graptoleberis. 



