TO TWELFTH ANNUAL REPORT. 



Sp. 3. Macrothrix tenuicornis, Kurz. 



(Plate C. Figs. 1, 1 a, 2, 3, and 12.) 

 (See Notes on Cladocera of Minnesota, p. 245.) 



The body is oval, produced posteriorly infa sharp point; the ab- 

 domen is strongly arched, while the upper outline'of the head is a 

 regular curve or slightly extended in front of the eye; the anten- 

 nules are long, nearly straight and a very little narrowed toward 

 the end, just in front of which is a series of short teeth; there is na 

 lateral spine, but a strong terminal one in addition to the sensory 

 filaments; the pigment spot is large, the eye small and the lobus- 

 opticus well separated from the ganglion; the antennae have a very 

 powerful basal joint; the elongated seta is very stout and densely 

 spiny, with a tooth at its flexure; two of the terminal seise are 

 spiny, for the basal half; the valves are beset with very long spines 

 in sets of three each, all having different positions; the abdomen is 

 nearly as in M. rosea, but the posterior margin has a series of long 

 sharp teeth; the mandibles are nearly completely exposed by the 

 arched anterior margin of the valves. 



The labrum, in this species, is an odd link between that of the 

 Daphnidas and Lynceidge. The basal segment is greatly enlarged 

 and is sub-triangular in outline, vvith a movable lip attached to the 

 inner free face; the typical daphnoid structure is preserved, but the 

 enlarged salient angle of the basal portion shows how the transi- 

 tion to the great triangular labrum of Aloua, etc., is made. In 

 young specimens the head is proportionately larger, the antennules 

 are broader at the tip, and the dorsal outline is less convex; the 

 marginal spines of the valves are also proportionally larger, as are 

 the appendages of the first and last pairs of feet. This is one of the 

 largest species of the genus, 0.75 mm. being the length. This 

 is very close to M. rosea but seems distinct. 



This form is quite common about Minneapolis, Minn., but is not 

 yet noted elsewhere in America. 



Sp. 4. Macrothrix pauper, Herrick. 



(Plate C. Fig. 4.) 



This species is described from a single specimen from L. Minne- 

 tonka, and I can add nothing to the very meager notice given 

 then. ^ 



1 Notes on some Minnesota Cladocera. 1881. C. L. Herrick. 



