106 AKmiAL REPORT. 



GENUS Macrothrix. 



{Big. — long hair.) 



Bibliography. — Macrothrix, Baird, Ann. Mag. Nat. Hist., XI, 87, 1843, and 

 XVII, 412; Trans. Berw. I^at. Hist, club, ii, 149. 



Daphnia, M. Edwards, Hist. Nat. Crust., iii, 384. 



Muller ( ?) Entomost. 



Lynceus, Desmarest, Cons. Gen. Et. Part. Crust., 376. 



Monoculus, Jurnine, Hist. Monoc. Generc, 



Acanthocercas, SchuJder Ericks, 1846. 



Macrothrix, Dana, Wilkes' Explos. Exp. Report. * 



Characters. — Head, beneath, either subacute or rather obtuse, anterior antennae 



rather long, pendulous from the beak, eye accompanied by a 



rather large black spot at the base of the attennse ; seta from first 



jomt of anterior branch of inferior antennae much longer than 



the others. 



Macrothrix agilis, Herrick. 



Description. — Head shield (as seen from above) very nearly Square; body car- 

 apace pear shaped; eye smaller than in Daphnia and accompanied with a rather 

 larare black spot similar to the obvious spot in Lynceus, but even larger. Superior 

 antennae very long in comparison with other members of the family. Inferior 

 antennae rather large, armed with large setae, of which the spine from the end of 

 the first joint is extremely elongate and plumose, nearly as long as the body. 

 This joint also has a small spine on the opposite or upper side of the ramus. 



The spine from the second joint is larger than in Dap>hnia. The final joint 

 bears a small spine also in addition to the three setae. (In the drawing both of 

 the rami have the elongate seta. This may be a mistake in the observation, 

 which was made in. some haste.) 



The jaws, feet, and posterior segments of the body, are similar, as far as 

 observed, to like organs in Daphnia. 



The lower and posterior part of the margin of the carapace bears a number of 

 long stout spines directed backward. The posterior body filaments, instead of 

 being simple or only plumose, are divided at the extremity into four small bristles, 

 forming a tassel or brush at the end. 



The intestine is not convoluted but is more abruptly curved and depressed near 

 the head than in Daphnia, thus approaching Dynceus. 



The motions of this interesting animal are Hvely and impetuous, it being 

 assisted by the long filaments of the antennae, which, with the body spines and 

 strong teeth of the shell, give to it a spider like aspect. 



This species difi:ers materially from any described by Baird, or any other author 

 with which I am familiar, but even if the elongate filaments should prove to be 

 commoa to both rami of the antennae, it mu^t fall in this genus. 

 Habitat. — Only observed in Rocky Lake, a small pool near East Minneapolis. 



Plate XIV. 



GENUS Lynceus, Muller. 



This genus was rejected by Dr. Baird who founded upon its remains a number 

 of genera, most of which were rejected in turn by Prof. Dana, who recognized 

 the following: 



