ART. 18 SYXOPSIS OF CALANOID CRUSTACEA — MARSH 9 



Each of the second basal segments of the male fifth foot (pi. 4, 

 fig. 4) is armed on the outer margin at about one-third its length 

 with a short hair. The exopod of the right foot is 2-segmented ; the 

 first segment is trapezoidal in form, with a stout spine at the outer 

 distal angle. The second segment is about three times as long as 

 its width; it has a stout spine about one-half the length of the 

 outer margin and three nearlj' equal terminal spines ; these spines are 

 nearly equal in length to the segment ; the inner spine is slightly the 

 longest and is slightly curved inward, while the other two are 

 straight. This segment has on its inner proximal angle a prominent 

 rounded pad covered with short hairs. 



The left exopod is 3-segmented. Segments 1 and 2 are about twice 

 as long as broad, and bear at the outer distal angles a rather slender 

 spine about equal in length to the segment. The third segment is 

 smaller than the first and second, about twice as long as its breadth, 

 and has three terminal spines ; of these spines the outer is the long- 

 est, being about two and a half times the length of the segment ; the 

 inner is small and rudimentary. 



Length, according to de Guerne and Eichard, 2-2.5 mm ; Schacht, 

 female, 1.7 mm, male, 1.4 mm; Herrick (1887), 2.3 mm. Those 

 measured by the author slightly exceed the figures of Schacht. 



Remarks. — The original description by Forbes was from material 

 collected near Normal, 111. He also found it in Iroquois County, 

 111. Herrick (1882) described his Potomoichetor fucosus from two 

 localities in Minnesota. Herrick (1887) notes its occurrence in 

 Alabama. De Guerne and Richard in 1889 recorded it from Port- 

 land, Oreg. Schacht added to previous records Havana, 111., and 

 Wyoming. Juday (1915) found it at Puerto Barrios and Los 

 Amates, Guatemala. Greaser (1931) found it in crayfish burrows 

 at Van Buren, Carter County, Ark. The author has found it in 

 collections made by Dr. E. A. Birge at Lake Charles, La., and Bertig, 

 Ark.; by Dr. V. E. Shelf ord in collections made near Gary, Ind. ; 

 and by H. K. Harring in the vicinity of AYashington, D. C. 



This is a somewhat erratic distribution, and it seems strange that 

 the species has not yet been found in intervening localities. It is not 

 evident why it has not been found in other places. There are few 

 data in regard to its annual distribution. Presumably the Illinois 

 collections were made in the summer. Most of the author's material 

 was collected in the fall, but one gathering was made in March. 

 Juday's Central American collection was made in February, but win- 

 ter collections in Panama have not contained this species. 



Apparently, so far as present knowledge is concerned, it is in the 

 United States practically a Mississippi Valley species, although we 

 have the records of Oregon and Wyoming. 



