7 o8 



FRESH-WATER BIOLOGY 



83 (23, 76) Antennules of female long, freely movable, usually inserted at 



anterior end of ventral surface of head. Kami of antennae 

 3- and 4-jointed. Intestine simple or convoluted. Hepatic 

 ceca usually wanting. Five or six pairs of feet. 



Family MACROTHRICIDAE Norman and Brady . . 84 



Abdominal process usually absent; rarely present (Ilyocryptus). Feet, 5 or 6 pairs, the 

 first two prehensile; the last, if present., rudimentary. Post-abdomen marked off from body, 

 usually large, often bilobed; anus terminal or lateral. Labrum usually with keel or marked 

 projection. Valves often crested. Fornices well developed. 



The members of this family are so various in form that it is hard to find many common 

 characters- yet the general appearance is always characteristic. The size and position of the 

 antennules will show the membership of every genus except Ilyocryptus; and there is no trouble 

 in recognizing that genus as belonging to the family. 



84 (95) Intestine convoluted 85 



85 (86) Valves with spine at supero-posteal angle. 



Small hepatic ceca. 

 Ophryoxus Sars 1861. 



Sole species. Ophryoxus gracilis Sars 1861. 



General form elongated, some- 

 what daphnid. Antennules long, 

 slender, fringed with numerous 

 hairs behind, lateral sense-hair 

 near base; olfactory setae unequal. 

 Antennae long, weak. Six pairs of 

 feet. Post-abdomen long, taper- 

 ing at apex, anus dorsal, post-anal 

 portion large with numerous short, 

 blunt, ciliated spines, the proximal 

 mere elevations bearing fine spi- 

 nules. Claws straight, with (usu- 

 ally) two stout basal spines. In- 

 testine with convolution in middle 

 of body; 2 small hepatic ceca. 

 Antennules of $ longer than 9 I 

 sense-hairs longer. Vasa deferen- 

 tia open on ventral (anterior) side 

 of post-abdomen about middle. 

 Color transparent, last foot often purple in old 9 Length, 9 to 



O.I MM. , 1 



FIG. uoo. Ophryoxus gracilis. 



Strong hook on first foot 

 2.0 mm.; $ , i.o mm. 



Widely distributed in lakes among weeds, 

 motion. Spine longer in young than adult. 



Swims with constant but rather feeble paddling 



86 (85) No such spine 87 



87 (92) Hepatic ceca present. 



88 



88 (89) Antennary setae 9 , ^ ; , c ^ c ^ ^ 5 ; valves narrowed behind and 



0-0-3 1-1-3 



prolonged into short tube. . Par Ophryoxus Doolittle 1909. 

 Sole species . . . Par Ophryoxus tubulatus Doolittle 1009. 



Form elongated oval; narrow crest on head and valves. Head rounded, rostrum well 

 marked; cervical sinus present. Valves thin, transparent; unmarked or faintly reticulated; 

 prolonged behind into a sort of tube, best seen from above; ventral margin with moderate 

 setae. Post-abdomen elongated, triangular; post-anal part long and slender, narrowed toward 

 apex somewhat as in Ophryoxus; bearing a few very small spines. Claws long, rather straight; 

 with 2 basal spines. Antennules cylindrical, slender; with basal sense-hair and three conspicu- 

 ously long olfactory setae. Antennae long, slender; basal joint annulated; setae not conspicu- 

 ously dissimilar. Feet, 6 pairs; the last rudimentary. Eye moderate, with few lenses; ocellus 



