NO. 1302. AMERICAN PARASITIC ARO ULIDJE— WILSON. 725 



In the male there are practically no lobes at all, but the copulatory 

 organs are well developed. The second joint of the second pair of legs 

 has on its posterior surface three rounded protuberances, two of which 

 are ventral, one near the base of the joint and one near the tip, while 

 the third one is dorsal and directl}' over the first at the base of the 

 joint. The flagella of these legs are longer than those of the first pair. 



The third legs carr}^ on the anterior side of the basal joint, a small 

 rounded knob drawn out at the tip into a soft tooth; the second joint 

 carries a similar protuberance, curved at the tip so that it bends over 

 and oflsets the tooth of the basal joint like the fingers of a pair of 

 forceps. The regular peg on the fourth legs appears to ]»e dou})le 

 instead of single. 



At the base of the abdomen on either side in the female is a small 

 ovate scale attached to the last segment of the thorax; this is lacking 

 in the male, and 3^et is one of the things which Thorcdl })roposed for 

 generic differences in A. purpureus. 



Color of alcoholic specimens green, whitish, or tawny. Length 13 

 mm.; length of carapace 8.6 mm.; width of carapace 8.5 mm.; length 

 of abdomen 3.9 nmi. ; breadth 2.7 mru. ; male about 0.8 this size. 



/rah J fat. — In the larger lakes of central and northern Sweden; in 

 Storsjon and other lakes of Jemtland on Cor m on/us. lavaretus Linnaeus, 

 and ThyriiaUus vulgaris Nilsson. In the salmon-lakes of Dalsland and 

 in the Vettern on Sahno trutta Linnaeus. Found on the external skin 

 instead of the branchial cavity. 



Dr. Nystrom in his Observations on the River-fauna of Jemtland 

 (1863) gives a fact in reference to this species which is of jDarticular 

 interest in its bearing on the general question of the relation ))etween 

 these parasites and their hosts. He says: "An unusually large species 

 of Argulas (referring to A. coregoni) fastens itself at certain times 

 in summer, in large numbers, on the Gwyniad {Coregonus)., and also, 

 though less readily, on the Grayling. Almost every fish has, during 

 this time, one or several of these bloodsuckers on its body, which liite 

 it till the })elly is quite drained of blood. The fishes then hurry in 

 crowds to certain parts of the lake, where probably the currents are 

 colder, and fall in large quantities into the nets which are there spread 

 for theip. This fishing lasts but a short time, perhaps two days onh^ 

 l)ut produces during that time in some localities several tons of fish." 

 (See the account of catostomi given on p. 651). 



{coregonus—ge.nQ.Yic name of its most common host.) 



ARGULUS MELITA Van Beneden. 

 Plate XXI II, ti^'. OB. 

 Argiilus melita V AN Beneden, 1891. 



Carapace elliptical; antero-lateral sinuses situated far back opposite 

 the sucking disks and cut in very deeply, leaving the cephalic area 



