508 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



IONE THOMPSONI Richardson.- 



lone thompsoni RICIIAHDSON, Proc. U. S. Nat. Mus., XXVII, 1904, pp. 75-78. 



Locality. North Falmouth, on Callianassa st'unpxon '/. 



Body of female longer than broad. 



Head deeply set in thorax, its anterior margin produced in a crenu- 

 lated border. The antero-lateral lobes of the frontal border extend 

 some distance beyond the sides of the head. The posterior portion of 

 the head is evenly rounded. The first antennae are three jointed; the 

 second pair are five jointed. 



All the thoracic segments are distinct, with distinct epimera 

 ("lames pleurales" of Giard and Bonnier), in the form of large 

 rounded lobes, not elongated. In the first two segments these epi- 

 meral lobes occupy the anterior portions of the lateral parts of the seg- 

 ments; in the third segment they are placed about the center of the 

 lateral margin; in the fourth and fifth segments they occupy more of 

 a posterior position; in the sixth and seventh segments they occupy 

 the entire lateral margin. Ovarian bosses are present on the first 

 four segments, along the anterior portion of the segment. 



The six segments of the abdomen are distinct, and are produced 

 laterally, each in a pair of elongated and jointed appendages, furnished 

 with numerous mammilliform, branching appendages, originating 

 from the posterior margin and extending downward. Thus there are 

 six pairs of appendages corresponding to the "lames epimeriennes du 

 pleon " of Giard and Bonnier. 



The pleopoda consist of four pairs of double-branched appendages 

 and one pair of single-branched appendages. a The inner branches of 

 the first four pairs fold over the ventral side, meeting in the median 

 line. These branches are all large and of nearly equal size and thickly 



jle longues digitations ramifiees qui le sont d'autant plus qu'elles sont plus pres de 

 la base. A la face ventrale (fig. 2) on voit deux paires de plopodes biram^s, dont 

 les rames sont de meme longueur, mais non de meme largeur: les endopodites sont 

 beaucoup plus larges en effet, surtout sur les premieres paires. Les uropodes ont la 

 forme ordinaire des autres especesdu genre, mais ils sont ici relativement beaucoup 

 plus courts et n'atteignent meme pas la moitie de la longueur du prolongement 

 pleural du sixieme somite du pleon. 



Le mille (fig. 10) mesure 4 mm. 5; il est grand, relativement a la taille de ses 

 congeneres d' Europe et il ne presente de differences que dans la forme des prolonge- 

 menta pleuraux du pleon: ils sont legerement attenues si leurs deux extn'mitc's, sur- 

 tout a la distale. Les pereiopodes des trois premieres paires ont des dactylopodites 

 aigus, tandis que ceux des autres paires sont ^mousses et rappellent la forme des 

 organes correspundants dans lafemelle. JULES BONNIER, Travaux de la Station zool. 

 de Wimereux, VIII, 1900, pp. 248-250. 



The young female of lone Ihowpsoni bas the last pair of pleopoda double-branched, 

 the two branches similar, however. The inner branches of the first four segments 

 are quite different from those of the outer branches, as is true of the adult female, 

 and lie folded over the abdomen as in the adult described. 



