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



GENUS LATONA Straus. 



Plate XXXV, Fig. 8. 



Body elongate, broad; head large and square, appeudaged below 

 with triangular laminse; fornices present. Antennules rather large. 

 The larger ramus of the antennse is two jointed and has an expanded 

 process at the base. The lower posterior angle of the shell has a pe- 

 culiar diverging set of setee. The shell is often ornamented with 

 numerous flecks of bright color. There is a copulatory apparatus in 

 the male. 



* Latona setifera Mueller, 



Is the only species, and is not yet recognized in Minnesota, but was 

 found by Professor Birge in Lake Michigan. 



Professor Birge mentions "one peculiarity not mentioned by any 

 European writer. There is a thick coat of short hairs on the head, 

 body and antennse. These hairs are 0.02 mm. or less in length, are 

 close set and give the outline a velvety appearance when seen by 

 transmitted light. It lives in clear water among weeds." 



GENUS LATONOPSIS Sars. 1888. 



Allied to Latona. Impression between head and thorax slight or 

 absent. Labrum devoid of plate like expansion. Antennule with a 

 long, plumose, straight or curved flagellum, articulated to the basal 

 part. Antenna with simj^le rami, the superior ramus bi articulate, 

 the inferior tri-articulate, as in Da]}hnella. Heart concave dorsally, 

 truncate anteriorly, the aorta arising on the ventral side. Shell gland 

 with three long branches. Male with simple copulatory organ, and 

 hook on first leg. Antennule long, slightly curved, armed with fine 

 teeth, resembling in general the antennule of Sida but having a 

 median projection near the base. 



* Latonopsis occidentalis Birge. 



Plate XXXVIII. 



Birge '91. 



Anterior outline of head forming a nearly straight line from the 

 antennules to the eye, where it passes by an abrupt curve into the 

 nearly straight continuous margin of the shell, which, however, be- 

 comes convex in old females. The ventral margin is continued into 

 the labrum and lacks the leaf-like appendages of Latona. Small 

 bilobed fornices are present. The ventral margin of the shell is 

 evenly rounded, passing without marked projection into the straight 

 caudal margin. The edge of the shell is fringed with long plumose 



