2IO General Notes, [February, 



species of Cyclops, say C. signatus (= C. coronatiis Cls.), we find 

 a form not at all rare but less abundant than C. tenuicornis with 

 which it seems to be constantly associated. In our investigations 

 we found Signatus almost constantly larger, in the same gathering, 

 than Tenuicornis. The only distinction, among those given by 

 either Claus or Brady, which is constant is the following: in Sig- 

 natus the last joint of the antennae has a longitudinal ridge shaped 

 like a pruning knife-blade extending beyond the end in a hook 

 with the proximal two-thirds of its length strongly toothed. (The 

 only other species which has teeth on the first joint is a species 

 allied to C. parens Her. found in Alabama, but this has no knife- 

 like ridge.) The two species agree in having the ridge which ex- 

 tend^ nearly to the base of the antenna ; they both have certain 

 series of spines arranged upon definite parts of the antennae ; both 

 have the circular series of spines on the basal joint of the fifth foot ; 

 in short there is a complete agreement even to the microscopic de- 

 tails — aside from the teeth above mentioned. 



Nevertheless it is possible to pick out Signatus from a glass of 

 the other form by its larger size and different color as well as to 

 detect a different relation in proportional length of the caudal setae, 

 etc. Close examination fails to discover an earlier stage of Signatus 

 while Tenuicornis is constantly accompanied by males and smaller 

 forms as well as the larval stages. The curious fact is demonstra- 

 ble that these species of the section of Cyclops with i /-jointed 

 antennae become sexually mature long before they are perfect 

 in form. In this species it is no uncommon thing to see females 

 of less than half the size of the adult with ova sacs. Indeed it is 

 common to meet larvae in which the antennae are as yet composed 

 of but few joints in a similar condition. This fact alters our con- 

 ception of a species considerably, inasmuch as it has been thought 

 sufficient to prove the maturity of a specimen to find the ^^^ sacs 

 developed. A glance at the literature of this family will suggest 

 that in more than one case a species has been founded upon a 

 larva which was simply prematurely gravid. 



In Cvlops seriillatiis the same fact is more easily observed, as 

 the species is so easily recognized as to be unmistakably at an 

 early stage. The van Montanus Brady, is not at all a variety due 

 to station as suggested by him but, if our observations are correct, 

 is the last form, in exceptional cases of the common species. It is 

 but a step further to show that as C timiicornis is a more advanced 

 stage of the small Cyclops forms with larval characters, so C. 

 signatus \^ but a post-imago of the former. In truth not only in 

 this species but in all others which we have had opportunity to 

 examine, there appear at favorable opportunities unusually large 

 and somewhat altered forms. These large, or post-imago stages 

 appear to be dependent upon abundance of food and a shallow, 

 warm habitat. 



The species considered identical with Dioptomns castor is abun- 



