I'LATYSCKMD.l-:. 320 



3. Thyropus rapax. 



Typliis rapnx, Edicanfs, Ann. dvs Sc. Nat. xx. p. 305; Hist, dcs Crust. 

 iii. p. 'J7. 



" This species is similar to T. ftrus. First i)airof gnathopoda having 

 the cai-pus not produced iuteriorly : second pair having the caiijus 

 produced inferiorly, nearly tis long as the propodos. Basos of the 

 fourth pair of pereiopoda not so largely developed as that of the 

 thinl pair. Laniclliforni rami of the three posterior pairs of pleo- 

 poda long, shai'p, and lanceolate. 



'' This species was found in the latitude of the Canary Islands." — 

 Edwards. 



2. PLATYSCELUS*, n. g. 



Cephalon transversely ovate. Pereion distended ; first segment nar- 

 rower than tht' cephalon. Pleon much narrower than the pereion, 

 having the fourth and fifth segments coalescing, the fifth and sixth 

 pairs of pleopoda being attached to the posterior margin ; sixth 

 segment and telson fused together, the posterior pair of pleopodu 

 being attached to the under surface near the middle of the seg- 

 ment. Supeiior antenme short, consisting of a peduncle and a 

 fiagellum. Inferior antennae not longer than the cephalon, con- 

 sisting of foui' joints, concealed beneath the cephalon, not folded. 

 Mandibles ^vithout an appendage. Third pair of pereiopoda having 

 the bases largely dilated, and the remaining joints shorter than the 

 bases ; fourth pair ha\nng the bases twice as large as the third, 

 the remaining joints not half so long as the basos ; fifth pair 

 membranous, a small tubercle representing the remaining joints. 

 Three posterior pairs of i)leopoda biramous, foliaccous, submem- 

 branous. Telson obtusely triangular. 



It is with considerable hesitation that I add this genus to the 

 family. I have only done so in consequence of Dana's distinctly 

 stating that in Dithyrus no portion of the three jjosterior pairs of 

 pereiopoda is developed beyond the basa ; in all other respects this 

 genus corresponds very closely with that. 



It appears to me to be not improbable that FlattjsceJus nuiy prove 

 to be the female of Typhis, from which it differs only in the form 

 of the superior and length of the inferior antenna;. 



1. Platyscelus Rissoinae, n. s. (Plate LII. fig. 9.) 



Cephalon rounded above anteriorly, and produced centrally down- 

 wards. Pereion greatly distended ; first two segments short. Pleon 

 much narrowei' than the pereion. Superior antennto having the 



* TrXrtrt's broadly dilated : aKcXos, leg. 



