NO. 1302. .1 MERICAN PARASITIC ARG ULID.¥^ WILSON. 739 



DOLOPS DISCOIDALIS Bouvier. 



Gyropettis kouari Bouviek, 1897. 

 Gyropeltis discoidalis Bouvier, 1899.^ 

 Dolops diKcnirlalis Bouvier, 1899.^ 



Carapace orbicular, wider than long; posterior .sinus broad and 

 about one-third the length of the carapace; lobes well rounded and 

 separated from the thorax so as to leave a space between. Abdomen 

 short and small. al)Out (».2, orbicular, somewhat narrowed anteriorly; 

 anal sinus slit-like and not extending more than one-third the length 

 of the abdomen. 



The second antenna? have a triangular spine on the basal joint which 

 IS fully as large as the joint itself, but there are no spines at the base 

 of the tirst antenna?. 



The teeth on the basal plate of the second maxillipeds are blunt and 

 rather widely separated. The two portions of the chela which termi- 

 nates each tirst maxilliped are of about the same size, and each is stifl'- 

 ened with chitin. 



The swinmiing legs just reach the edge of the carapace; each of the 

 basipod joints of the posterior pair carries a very large flap on its pos- 

 terior margin, those on the tirst joint being of the typical boot shape. 



Each of the three anterior pairs of legs are furnished with flagella, 

 those of the third pair being small, but fulh' developed. 



Color. — Grayish green, with large rounded light-colored })lotches 

 arranged parallel with the margin of the body. Around the paired 

 and median eyes these blotches fuse into large whitish areas. 



Length, 11.8 to 14 nun.; length of carapace, 10 to 12 nun.; breadth 

 of carapace, 10.6 to l-t mm. ; length of abdomen, 3 to 3.. 5 mm. ; breadth 

 4 to 4.3 mm. 



Hahltat. — From the Rio Nuba, in Brazil, on a species of Platysoma, 

 called by the natives ** Doncella" (^//6'("6'/^vfc///.s' = disk-shaped, alluding 

 to the carapace). 



From a careful comparison of the genera and species here described 

 we are enabled to deduce the following as the probable developmental 

 history of the family. The primitive form from which the genera of 

 the family have l)een developed through a greater or less adaptation 

 to parasitic habits must have l)een very simihir to the free copepods, 

 a form possessing a moderate-sized, flattened carapace, three free tho- 

 racic segments, and a more or less lamellar a])domen. The anterior 

 maxillipeds terminated in an ordinary-sized chela; there was no pre- 

 oral sting; the mouth parts were very little, if at all, protrusilfle, and 

 the ventral surface was unarmed with spines. 



We find no species corresponding with this at the present time, 

 because the first change, and one that must have taken place very 

 quickly after the beginning of parasitic habits, was the making of 



