104 AKNUAL REPOBT. 



of the head seems wider and less arched than in other species. Jaws long and 

 ending in a circle of fine teeth. Feet as iapidex. 



Seen from above the carapax of the body is found to consist of three pieces 

 The first, which might be termed the scutella, is a small shield adjoining the 

 head, and the two principal pieces or valves of the shell may be considered as 

 appendages of the scutella. These pieces may be compared to the tergum and 

 pleuron of trilobites. 



The structure of the beak and its relation to the head is more clearly seen than 

 in most of the Daphnise. The head shield as seen from below is transversely 

 sub-oval. Directly in front and very near the anterior margin of the skull is an 

 eye, filling a circular elevation reaching the anterior margin, and sending off 

 posteriorly a ridge or straight partition which divides the lower aspect of the 

 head into two basin -like cavities. This ridge terminates in the beak which car- 

 ries the superior antennae and the black spot which Huxley calls an ocular pig- 

 ment, but by other authors is thought to be attached to the auditory apparatus, 

 and is termed by Dana the "otolites", following Schoder in so consideriug it. 

 (See Plates X. and XI.) 



Daphnia Mucronata. 



Bibliography . — Daphne mucronata, Muller, Zool. Dan. Prod., No. 2404, 1776. 



Dapnia mucronata, Muller, Entomst. , 94. 



Desmarest. Cons. gfen. Crust. 374. 



Latreille, Hist. Nat. Crust., IV., 229. 



Bosc, Man. d'Hist. Nat. Crust., ii., 281. 



M. Edwards, Hist. Nat. Crust, iii., 382. 



Baird, Trans. Berw. Nat. club, ii, 148. 



Monoculus mucronatus, Gmelin, Linn. Syst. Nat., 



edit. 14th, i., 3,000, No. 28. 



Manuel, Enc. Mith., t. 265, f. 19. 



Jurine, Hist. Nat. Monoc. 137, t. 14, f. 1, 2. 



Monoculus bispinosus, De Geer, Mem. Servir. Hist. Ins., YIL, 

 463, 1778. 



Fabricius, Ent. Syst,, iii., 493. 



Daphnia bispinosa, Koch, Deutsch. Crust., h. VHI., t. 1. 

 Description. — General shape, as seen from above, oval. Lower margin of the 

 carapax straight, terminated posteriorly by a curved spine. Head triangular, 

 obtuse in front. Eye large. Superior antennae small. Inferior antennae long. 

 Lower part of the carapax ciliated. Color dark. Dr. Baird says that the 

 form of the head varies in this species, being sometimes rounded and at others 

 terminated by a sharp, somewhat curved point directed upwards. 



I have not observed in any of the many specimens seen a sharply pointed head; 

 and though this point casts some doubt on the identification, every other point 

 in his description seems to agree very well with our species, which I find no war- 

 rant for separating from D. mucronata var. obtuse rostrata. 



Habitat. — Sandy Lake (East Minneapolis), Clark's Lake, Grassy Lake, etc. 

 (See Plnte XII.) 



Daphnia (Ceriodaphnia, Dana) Reticulata. 



Bibliography. — Monoculus reticulatus, Jurine, Hist. Nat. Monoc, 139, t. 14, 

 f. 3, 4. • -^ 



