no. 3628 GENUS PARANTHESSIUS — HUMES 5 



Labrum, mandible, paragnath, first maxilla, and second maxilla as 

 in female. Maxilliped (fig. 29) slender and 4-segmented, assuming 

 that proximal part of claw represents a fourth segment. First segment 

 unarmed. Second segment bearing two inner setae, innermost with 

 sclerotized basal portions (fig. 30), and row of spinules on posterior 

 surface. Third segment small and unarmed. Recurved claw 172m along 

 axis, with slight indication of division about midway; terminal lamella 

 very narrow; two unequal setae on proximal part of claw. 



Postoral area as in female. 



Legs 1-4 as in female, with same spine and setal formula. Last 

 segment of endopod of leg 1 (fig. 31) showing very slight sexual di- 

 morphism, with more numerous terminal spinules and outer fringe on 

 spine more strongly spinulose than in female. 



Leg 5 (fig. 32) with free segment 33m x 13m, terminal seta 62m, and 

 subterminal inner spine 15m and without lamellae. 



Leg 6 (fig. 33) a posteroventral flap on genital segment bearing 

 two naked setae 29m and 38m long, with a row of minute spinules 

 near insertion of longer more anterior seta. 



Spermatophore not seen. 



Color in life like that of female. 



Etymology. — The specific name protothacae is formed from the 

 generic name of the host. 



Comparison with related species. — Following the views of Illg 

 (1949) and adding information from Bocquet and Stock (1958, 1958a, 

 1959), Gotto (1961) regarded the genus Paranthessius as embracing 21 

 species. Stock (1964) has, however, removed six of these species to 

 the genus Scambicornus Heegaard, 1944. These are S. prehensilis 

 (Sars, 1918), S. robustus (Thompson and A. Scott, 1903), S. serendibi- 

 cus (Thompson and A. Scott, 1903), S. propinquus (Nicholls, 1944), 

 S. finmarchicus (T. Scott, 1903), and S. tenuicaudis (Sars, 1918). A 

 recently described form, P. colmani Reddiah, 1960, must be added to 

 the genus, bringing the number of currently recognized species to 16. 

 For the purpose of the description of P. protothacae and the following 

 new species, Paranthessius is held to consist of these 16 species, 

 although it is recognized that many problems exist in the determina- 

 tion of the generic limits and that several authors (for example, 

 Monod and Dollfus, 1932; Illg, 1949; Sewell, 1949; Bocquet and Stock, 

 1957; and Reddiah and Williamson, 1959) have variously interpreted 

 the scope of the genus. 



Nine species of Paranthessius have a. distinct beak on the rostrum 

 and may thus be distinguished readily from P. protothacae. These 

 are: P. columbiae (Thompson, 1897); P. panopeae Illg, 1949; P. 

 tivelae Illg, 1949; P. nasutus (Edwards, 1891); P. pectinis (Pesta, 



