120 U.S. NATIONAL MUSEUM BULLETIN 236 



account, nevertheless, for a certain degree of variability of this 

 important structure in the various forms attributable to the genus 

 Porcellidium. I am inclined, therefore, to consider Bocquet's sub- 

 divisions of this "supraespece" with some reserve and I have arranged, 

 at least provisionally, the various "species" defined by Bocquet 

 under the heading Porcellidium viride. 



In addition to the species listed above, a new species will be described 

 below as Porcellidium malleatum. The new form can be fitted in 

 the following way into the key given by Lang (1948, p. 419) for the 

 females of this genus. The inclusion of Porcellidium fulvum in this 

 key is on Nicholl's authority (1941). 



Key to the Females of Porcellidium 



1. Furca pointed, i.e., furca narrowing into a point or cut off obliquely . . 2 

 Furca not pointed, cut off squarely or rounded 5 



2. Margin of body, especially cephalic somite, set with hairs. 



P. brevicaudatum Thompson and A. Scott 

 Margin of body without hairs 3 



3. Furca cut off obliquely P. ovatum Haller 



Furca gradually narrowing 4 



4. Furca rounded at the apex P. ravanae Thompson and A. Scott 



Furca cordate P. tenuicauda Claus 



5. Greatest diameter of furca at about halfway its length 6 



Greatest diameter of furca at the apex of furca with parallel walls ... 8 



6. Furca quadrate, about as long as wide P. fulvum Thomson 



Furca elongate, twice (or more) as long as wide 7 



7. Body twice as long as broad; big (about 1 mm. length) species. 



P. affine Quidor 

 Body V/z as long as wide, small (0.60 mm.) species. 



P. malleatum, new species 



8. 5th legs covering the whole length of the furca and, curving round the 



furca, almost touching in the median line . P. interruptum Thomson 



5th legs covering the length of abdomen with furca, not meeting in the 



median line 8 



9. Furca broadening distally, at apex twice as wide as at insertion. 



P. scotti Pesta 



Furca with almost parallel walls 9 



10. Internal seta of endopodite leg 1 inserting proximally . . P. viride Philippi 

 Internal seta of endopodite leg 1 inserting distally . . P. clavigerum Pesta 



Porcellidium malleatum, new species 



Figures 40-44 



Material. — Loc. 431, 1 ad. 9, 0.57 mm.; 2 ad. cf d', 0.47 and 

 0.48 mm. 



Description. — The following is based on the female holotype and 

 the male allotype (0.48 mm. length), both of which have been dis- 

 sected and mounted. The second male has been labelled as paratype. 



Adult female, total length 0.57 mm., greatest diameter 0.39 mm. 



