84 U.S. NATIONAL MUSEUM BULLETIN 260 



Kelationshtp. — TrypJiosella metacaecvla has the well-developed ac- 

 cessory tooth of the dactyl of ^athopod 1 typical of the genus Tme- 

 tonyx discussed above. In J. L. Barnard's (1962a) key to the species 

 of '■''T rypTioscC and Tmetonyx^ TrypTiosella metacaecula is shown to 

 have affinities with ''Tryphosa'' trigonica (Stebbing, 1888) ; 'T." 

 groenJandica Schellenberg (1935) and "7"." intermedia Schellenberg 

 (1926a) . Gnathopod 1 of "7"." trigonica is very slender, scarcely sub- 

 chelate, the epistome broadly protrudes and the dorsal process of pleo- 

 nite 4 is large and acutely erect. The epistome of "7"." intermedia 

 strongly protrudes and coxa 1 scarcely tapers. The peduncle of uro- 

 pod 2 of "7"." groenlandioa exceeds in length that of uropod 1 and 

 extends as far as the apices of the rami of uropod 3. 



Tryphosella metacaecula is remarkably similar to '■'■Tmetonyx'^'' 

 caeculics (Sars, 1895, pi. 35, fig. 1), hence the derivation of its name. 

 Both share a slight dorsodistal hump and protusion on article 1 of 

 antenna 1. The upper lip of T. metacaemda is damaged but is be- 

 lieved to be reasonably well reconstructed. It resembles that of 

 "7^." caeculus. Tryphosella metacaec^ila differs from 'T." caeculus 

 in the chelate palm of gnathopod 2, the subtriangular (not dorsally 

 rounded) process of pleonite 4 (perhaps a character subject to aging 

 or sexual dimorphism), the 2- (and not 4-) articulate accessory 

 flagellum, the slightly shorter pereopods 1-5, the stouter uropod 3, 

 the deeper notches of tlie telsonic apices and especially by the pos- 

 teriorly beveled and tapering coxa 1. Coxa 1 of Sars' species has 

 not been figured in a dissected and flattened view but presumably 

 resembles that of T, metacaecida. 



Trypliosella metacaecula is an unusual "tryphosa" because of the 

 shortened third mandibular palp article but so many deep-sea lysianas- 

 sids have this condition that one may wonder whether it has any 

 generic significance (as J. L. Barnard, 1962a, believed in his estab- 

 lishment of the genus Elimedon). Perhaps low concentrations of 

 detritus in the deep sea reduce the need for a long setose mandibular 

 palp as a cleaning organ. Its condition in "T"." caeculus is not de- 

 scribed by Sars. 



The slightly thickened first maxillary spines are of significance 

 to the discussions presented elsewhere on the relationships between 

 various species of ''^Tryphosa'''' and Hippomedon. 



