Pellidiidce, to which family it was indeed referred by Glaus; but the structure of 

 the several appendages is very different, and more approaches that in the fol- 

 lowing family, the Idyidce. 



Gen. 20. PorCellidlUm, Glaus, 1860. 



Syn: Thyone, Philippi (not Oken). 



Generic Characters. Body short and flattened, with the cephalic segment 

 very large and expanded; rostrum broad, lamellar, not defined at the base. 

 Epimeral plates of the first 2 free segments of metasome tongue- shaped, those 

 of 3rd segment in female rudimentary, in male well developed. Last segment in 

 both sexes without any trace of epimeral plates, and in female imperfectly defined 

 behind. Urosome short and flattened, in both sexes composed of only 2 segments, 

 the anterior one large and lamellar, the posterior small, subquadrate. Caudal 

 rami more or less lamelliform, with very short apical seise. Eye present, of usual 

 structure. Anterior antennae short, 6-articulate, in male strongly prehensile. 

 Posterior antennae with the outer ramus uniarticulate. Mandibles very strong, 

 with the palp excessively large, lamellar, indistinctly 3-lobed, and provided out- 

 side with numerous thick plumose seta?. Maxillae with the palp normally developed. 

 Anterior maxillipeds comparatively short and stout, with 2 unequal setiferous 

 lobes inside, terminal joint rather broad, incurved, with several strong spiniform 

 setse on the tip. Posterior maxillipeds rather small, 3-articulate, 1st joint pro- 

 vided in front with an oval ciliated lamella, 2nd joint tapered distally, with a 

 short deflexed lobe inside, last joint very small, with 2 short incurved claws at 

 the tip. First pair of legs with the outer ramus 3-articulate and very delicate, 

 being edged outside with soft plumose setae, inner ramus biarticulate, 1st joint 

 large and triangular in form, last small and armed with 2 subequal claws, densely 

 fimbriate on one side. Natatory legs with both rami 3-articulate, inner ramus in 

 1st pair much larger than in the 2 succeeding pairs. Last pair of legs in female 

 distinctly biarticulate, distal joint large, lanceolate; those in male much smaller, 

 uniarticulate, sub-quadrate, terminal edge aculeate. 



Remarks. This genus was established as early as the year 1839 by 

 Philippi, to include a Mediterranean species, T. viridis ; but as the name Thyone 

 proposed by him had been previously appropriated by Oken for a genus of Holo- 

 thuroida, it was changed by Glaus to Porcellidium. The latter author records 3 



