6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



1909); P. rostratus (Canu, 1891); P. haploceras Bocquet and Stock, 

 1959; P. barneae (Pelseneer, 1929); and P. colmani Reddiah, 1960 



The new species may be separated from the remaining seven species 

 as follows: P. anemoniae Claus, 1889, has an elongated segment in 

 leg 5 (about 5:1 in Bocquet and Stock, 1959a, fig. 5d) and the second 

 antenna has three terminal claws; P. cynthiae (Brian, 1924) has the 

 caudal ramus equal to the length of the last two postgenital segments 

 and the last segment of the second antenna much longer than the 

 penultimate segment; P. myxicolae Bocquet and Stock, 1958, has re- 

 curved spines on the first and second segments of the first antenna 

 and three terminal claws on the second antenna; P. parvus (Norman 

 and T. Scott, 1905) has jointed setae (no claw) on the last segment 

 of the second antenna in the female; P. perplexus Illg, 1949, has an 

 ellipsoid rounded process on each side of the genital segment in the 

 female; P. saxidomi Illg, 1949, has a reduced maxilliped in the female 

 (length less than half the basal segment of the second maxilla), the 

 basis of legs 1-3 with stout spinules, the last segment of the endopod 

 of leg 4 with the inner spine nearly 2.5 times the length of the outer 

 spine, the segment of leg 5 in the female with a rounded expansion at 

 the base and the two terminal elements subequal in length, the male 

 maxilliped with a modified seta on the second segment, and the male 

 genital segment with two pairs of rows of spinules; and P. validus 

 (Sars, 1918) has a caudal ramus that in the female is only slightly 

 longer than wide. 



Paranthessius mesodesmatis, new species 



Figures 34-43 



Type material.- — 14 99 and 16 cf cf from the mantle cavity of 39 

 Mesodesma donacium Lamarck purchased in the fish market at Val- 

 paraiso, Chile, Aug. 4, 1966. (These pelecypods presumably came 

 from Vina del Mar, near Valparaiso.) Holotype female, allotype, and 

 24 paratypes (11 99, 13 cf d 1 ) deposited in the United States National 

 Museum, and the remaining paratypes (dissected) in the collection of 

 the author. 



In the following description those features not mentioned may be 

 assumed to be essentially like those of the previous species. 



Female. — Body (figs. 34, 35) with tumid prosome. Length (not 

 including setae on caudal rami) 1.49 mm (1.40-1.63 mm) and greatest 

 width 0.64 mm (0.48-0.77 mm), based on 8 specimens measured in 

 lactic acid. Dorsoventral thickness of prosome about 0.66 mm in a 

 specimen 1.50 x 0.64 mm. (One female less tumid than the others, its 

 dimensions 1.47 x 0.47 mm, with dorsoventral thickness of 0.42 mm.) 

 Ratio of length to width of prosome 1.38:1. Segment of leg 1 very 



