2 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



The discovery of these two new copepods extends the eastern Pacific 

 range of the genus as far south as central Chile. 



The study of the specimens has been aided by a grant (GB-5838) 

 from the National Science Foundation. 



All figures have been drawn with the aid of a camera lucida. The 

 letter after the explanation of each figure refers to the scale at which 

 it was drawn. The abbreviations used are: Ax = first antenna, 

 A 2 = second antenna, L=labrum, MD= mandible, P=paragnath, 

 MXi= first maxilla, MX 2 = second maxilla, MXPD=maxilliped, and 

 Pi=leg 1. 



I thank Prof. Jose Stuardo of the Universidad de Concepcidn, 

 Concepci6n, Chile, for the identifications of the two pelecypod hosts. 



Family Lichomolgidae Kossmann, 1877 



Genus Paranthessius Claus, 1889 

 Paranthessius protothacae, new species 



Figures 1-33 



Type material.— 11 99 and 10 cf c? from the mantle cavity of 59 

 Protothaca thaca Molina purchased in the fish market at Iquique, 

 Chile, Aug. 23, 1966. (These pelecypods probably came from Punta 

 Guanillos, 21°15'S, 70°07 / W, south of Iquique.) Holotype female, 

 allotype, and 16 para types (8 99, 8 cf cf ) deposited in the United 

 States National Museum, and the remaining paratypes (dissected) 

 in the collection of the author. 



Female.- — Body (figs. 1, 2) moderately slender, about three times 

 longer than wide, with prosome not greatly thickened dorsoventrally. 

 Length (not including setae on caudal rami) 1.62 mm (1.47-1.78 mm) 

 and greatest width 0.54 mm (0.50-0.61 mm), based on 10 specimens 

 measured in lactic acid. Dorsoventral thickness of prosome about 

 0.45 mm. Ratio of length to width of prosome 1.9:1. Segment of leg 

 1 separated from head dorsally and laterally by a distinct furrow. 

 Epimeral areas of metasomal segments as illustrated. 



Segment of leg 5 (fig. 3) 91/x x 135m- Between this segment and 

 genital segment a weak ventral intersegmental sclerite, its sclerotiza- 

 tion more evident laterally (fig. 4). A median prominence in front of 

 segment of leg 5 (figs. 4, 5). Genital segment as long as wide, 216m x 

 216/x, in dorsal view anterior half laterally expanded with rounded 

 margins and posterior half narrower and tapering slightly posteriorly 

 with straight margins. Areas of attachment of egg sacs located dorso- 

 lateral^, each area (fig. 6) bearing small seta 13m long and spiniform 

 process 6/x. Three postgenital segments 78m x 120m, 70m x 109m, and 

 114m x 99m, from anterior to posterior. Anal segment with postero- 

 ventral margins unornamented. 



