30 PROCEEDINGS OP THE NATIONAL. MUSEUM vol. 80» 



of this species so abundant in January and February at Woods 

 Hole that they far outnumbered the adults, showing that they breed 

 freely there in winter. This species ranks next to Calanus -jinrnwr- 

 chiaas in abundance in the Gulf of Maine. It is very much les» 

 abundant in Chesapeake Bay, and its percentage mark only rarely 

 gets above 5, and is frequently less than 1. This is what would 

 naturally be expected of a northern form when found so far south. 

 In a plankton series collected continuously across the North Atlantic 

 by Herdman, this species was very common around both shores and 

 was also taken in mid-ocean. 



PSEUDODIAPTOMUS CORONATUS Williams 

 Pl^TE 2 



Pseudodiaptomus coronatus Williams, Amer. Nat, vol. 40, p. 641, figs. 1-7, 

 1906.— Shabpe, Proc. U. S. Nat. Mus., vol. 38, p. 412, fig, 4, 1911. 



General characters. — Abdomen of male with four segments, of 

 female with three segments; genital segment of female swollen^ 

 asymmetrical, and covered with irregular patches of spines. Fifth 

 legs of female with four segments and a stout terminal spine; fifth 

 legs of male as shown in Plate 2, J. 



Specific characters of female. — Body slender, anterior portion, 

 elliptical, two and a half times as long as wide ; head separated from 

 first thoracic segment and evenly rounded anteriorly. Posterior 

 body quite asymmetrical, the left side more fully developed than the 

 right. Genital segment much swollen, with numerous irregular 

 patches of spines and bristles and a pair of long pointed flaps 

 extending behind the genital orifice. Abdomen of three segments, 

 the two basal ones irregular, the terminal one more symmetrical. 

 Left caudal ramus considerably longer than the right and curved 

 outwards, six and a half times as long as wide ; right ramus straight 

 and only five and a half times as long as wide. 



The plumose setae at the tips of the rami are each jointed near 

 the center and swollen in front of and behind the joint. The same 

 is true of the setae of the swimming legs, as was shown by Williams, 

 but neither he nor Sharpe mentioned the jointing in the caudal setae. 



Every female with egg sacks carried a large left sack, containing 

 about 25 eggs, and a minute right sack containing only two eggs. 

 But Sharpe found one or two females at AVoods Hole with egg sacks- 

 about equal in size, and a single female that carried one large sack. 



First antennae 20 to 22 jointed, the jointing so indistinct as to be 

 practically invisible in places; when reflexed the first antennae do 

 not quite reach the posterior margin of the front body. Second 

 antennae with an outer ramus much longer than the inner one and 

 3-segmented, the basal segment much shorter than either of the other 

 two, the terminal segment ending in three very long plumose setae. 



