162 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 41. 



ing, the labrum thus appearing fenestrated. Maxillae with three 

 teeth. Thoracic appendages or legs six, conforming closely to family 

 type. Postabdomen long, tapering, triangular; armature very weak, 

 consisting of a double row of a few tiny spines distally upon upper or 

 posterior border, and laterally of a few fasciculi of spicules. Caudal 

 claw long, slightly curved, with two small spines at base; claw cili- 

 ated on both concave and convex borders. 



Intestine coiled, hepatic c£eca present. 



Male. — Form similar to female. First antennae or antennules 

 each with long sensory seta; second antennae each with additional 

 seta upon each of the first and second segments of the lower or inner 

 ramus, therefore, setae WV"; spines WV- Hook upon first leg. 

 Postabdomen almost smooth; sperm duct terminal. 



Though resembling Opliryoxus m side view quite remarkably, it 

 is necessary to establish this genus as the following parallel shows. 



Parophryoxus. 



Ophryoxus. 



General aspect 



Head 



Dorsal margin 



Ventral margin 



Posterior margin 



Sides 



Keel 



Antennules 



Antennae, female 



Labrum 



First leg 



Postabdomen 



Caudal claw 



Rectal cfeca 



Opening of sperm duct 



Ellipsoidal 



Evenly, convexly rounded 



Sloping downward and produced with 

 out spine. 



Sinuate, middle third setigerous 



Low, and at end of tubular extension . 



Concave 



On head and body 



Almost smooth 



Set^ 0023, spines ?M 



003 001 



"Without fleshy organs, fenestrated. . . 



Without maxillary process 



Armature obsolescent 



Convex border ciliated 



Absent 



Terminal 



Quadrangular. 



Truncated, concave. 



Directed upward and with prominent 



spine. 

 Straight, setigerous throughout. 

 High, no extension of test. 

 Convex. 

 Lacking. 

 Heavily bristled. 



set^o_oo3, i^^^gioi, 



113 ^ 001 



With fleshy organs, not fenestrated. 

 With maxillary process. 

 Armature very strong. 

 Convex border smooth. 

 Present. 

 Middle of anterior border. 



Type-species. — P. tuhulatus Doolittle. 



The name was chosen to indicate its relationship to other Lyn- 

 codaphniidae by Prof. E. A. Birge, to whom also the writer is in- 

 debted for calling his attention to the proper place among the 

 Cladocera of specimens of this genus and to important characteristics. 



PAROPHRYOXUS TUBULATUS DooHttle. 



Plates 13, 14, 15, and 16. 



Parophryoxus tubulatus Doolittle, Proc. Biol. See. Washington, vol. 22, 1909, 

 p. 153. 



Female. — Length 1.15 mm.; height one-half to two-thirds the 

 length. General form, long oval. Upper and lower margins curved 

 nearly symmetrically; however, the middle third of lower margin 

 flattened, sinuate, bearing ciliated setae, long in the middle part and 

 diminishing rapidly anteriorly and posteriorly. The convergent 

 dorsal and ventral margins and two sides produced to form a rather 

 conspicuous tube posteriorly, the open end of which constitutes the 

 free posterior margin. Posterior margin one-fifth to one-seventh of 



