1914.] NATURAL SCIENCES OF PHILADELPHIA. 37 



of this species." It is interesting to note the measurement of the 

 following five females taken at random: 



No. 1 2.5 mm. 



No. 2 .2.51 mm. 



No. 3 2.21 mm. 



No. 4 2.50 mm. 



No. 5 2.47 mm. 



This gives an average measurement of 2.43 mm. for representatives 

 of the species from this locality — less than .1 mm. difference in size 

 from European forms. Taking Forbes' figures and the above 

 together, we get an average measurement of 1.88 mm. 



The color, a blue-gray, occasionally nearly black, is most prominent 

 in the stylets and last abdominal segment, the second, third, first 

 half of the fourth, ninth and tenth segments of the first antennae 

 ( 9 ) and in irregular transverse bands, usually four, on the cephalo- 

 thorax. The remaining portions of the animal are nearly colorless 

 or a pale shade of yellow, though I have frequently noted individuals 

 in which they were a bright blue-green. 



, The species seems to be one of the commonest not only in America^ 

 but all over the world. Forbes found it "in all localities examined." 

 In nearly all the lists of crustaceans to which I have access it is 

 recorded as a common but rarely abundant variety. 



Kofoid records it as "numerically the least important of the 

 dominant members of the genus in our plankton" (Illinois River). 

 I have found it to be one of the commonest of the Cydopidce. 



Miss Walker has studied the species in Todd's Pond, Oregon^ 

 where she found it to be, with Cyclops serrulatus, second in abundance 

 after Cyclops prasinus. 



In collections made during the summer of 1909, at Lake Winne- 

 pesaukee and in the vicinity of Cambridge, Mass.. in March and 

 April, 1910, C. albidus was a common but not an abundant form. 



Subgenus ORTHOCYCLOPS Forb33. 



Cyclops modestus Herrick. PI. II, figs. 0-11. 



Cyclops modestus Herrick, '83a, p. .500. 



Cyclops modestus Herrick and Turner, '9.5, pp. 108, 109, pi. XXI, figs. 1-5. 



Cyclops modestus Mansh, '93, pp. 213, 214, pi. V, figs. 10-13. 



Cyclops capilliferus Forbes, '93, pp. 248, 249, pi. XL, figs. 14-17; pi. XLI, 



fig. 18. 

 Cyclops modestus Forbes, '97, pp. .51-53, pi. XV, fig. 4; pi. XVI, figs. 1-3. 

 Cyclops modestus Byrnes, '09, pp. 26, 27, pi. XI, figs. 4 and 5. 



Specific Description.- — The shape of the cephalothorax is very 

 characteristic in this species (PI. II, fig. 6). The first segment reaches 



