NEW CRUSTACEAN GENUS. 765 



pair the endopod may be a good deal sliortei* than the exopod, or, 

 as in the specimen figured, nearly equal to it ; both rami are un- 

 segmented. In the second pair also the i-ami are unsegmented, 

 and the endopod is from about one-half to two-thirds as long as 

 the exopod. In the third and fourth pairs the rami are subequal 

 and the endopod is divided into two subequal segments. The 

 basal lobe of the protopodite in the fourth pair is tongue-shaped, 

 with a slight protuberance at the base of its distal edge. 



Dimensions of Rolotype in millimetres. 



Length of body to tip of abdominal lobes 20'0 



Total length to tip of cai'apace wings 26"0 



Breadth of head 2-5 



Length of thoracic region 8*0 



Breadth of thoracic region 2*5 



Breadth of wing at base 1*8 



Greatest breadth of wing, at about 8 mm. from base 4'8 



Length of abdominal lobes 6 'S 



Greatest breadth of abdominal lobes 1 '3 



Length of antennules and antennre, about 0"13 



Length of oral cone 0"5 



Greatest diameter of sucker 1*1 



Length of second leg 1 "8 



Diameter of eyes, about 0' 1 



Distance apart of eyes, about 0'45 



Locality. — Corumba, on the Paraguay River, Matto Grosso, 

 Brazil. Four female specimens taken (in company with Dolops 

 longicaucla) on the fish known as " Dorado " (probably a species 

 of Salminus). 



Rolotype. — Female, No. 92.10.24.2 in British Museum Register 

 of Crustacea. 



Affinities. — In having the so-called maxillse or first maxillipeds 

 modified into suckers this species diS"ers from the genus Dolops, 

 and in possessing anteniiules and a preoral papilla it differs from 

 Chonopeltis. From all the species hitherto referred to Argulus it 

 diflfers in (1) the remarkable form of the lateral wings of the 

 carapace ; (2) the length of the abdominal lobes and the absence 

 of furcal rami, in which characters it resembles some species of 

 Dolops ; (3) the entire absence of conspicuous spines or hooks on 

 the under side of the body and appendages, in which it resembles 

 Chonopeltis ; (4) the vestigial condition of antennules and 

 antennge ; (5) the absence of a spine or sting on the preoral 

 papilla; (6) the absence of the usual radial supports on the disc 

 of the suckers. Some of these characters, especially Nos. 1, 3, 

 and 6, are possibly not of great systematic importance, but 

 together they seem to show that the new form is less closely 

 related to any of the species included in the genus Argulus than 



