544 



Distribution: R. minor is more widely distributed than R. brevicau- 

 datum. It is found circumtropically; in the Atlantic Ocean has been 

 reported up to 60° N. in the region of the Irminger [sic] Sea. Though 

 rather common in the eastern half of the Atlantic Ocean, there are no 

 reports from the western part along the American coastline. Neither has 

 it been reported from the Mediterranean Sea. Reproduction occurs year 

 round. 



XXII. Family PLATYSCELIDAE Bate, 1862 



Mostly very small (4-6 mm) crustaceans. The body is wide, generally has 

 a thick integument, and is flattened dorsoventrally. The pleon is narrower 

 than the pereon and may bend underneath it. In this case the operculiform 

 2nd segment of pereopods V and VI close the unprotected space from 

 the ventral side of the body and the crustacean assumes the shape of a 

 compact smooth egg. The head is high, short, somewhat broader than 

 the pereon, with a small beak-shaped roundish triangular process in the 

 ventral part. The large eyes occupy a large part of the surface of the 

 head. Antennae I of males have a three-segmented peduncle and a four- 

 segmented flagellum; the 1st segment is strongly bulged, curved in the 

 middle part anteriorly, and is uniform in width almost throughout its 

 length. Antennae II in males are long, thin, and folded five times, in 

 439 females short and few-segmented. The mandibles are short and have a 

 broad cutting edge; only the males have a palp. Maxillae I and II have 

 large wide lobes. 



Pereopods I and II are simple or have subchelae or chelae. The 2nd 

 segment of pereopods V and VI is markedly broadened and operculiform, 

 especially in pereopods VI; in pereopods VI this segment has a groove 

 inio which the edges of the telson and uropods fit when the crustacean 

 folds itself; the distal segments are small and together several times 

 shorter than the 2nd segment. Pereopods VII consist of a twisted 2nd 

 segment and one-two rudimentary distal segments. The endopodite of 

 uropods III is usually fused with the basipodite. The telson is broad, 

 triangular, and usually fused with the last urosomite. 



The family includes five genera. 



KEY TO GENERA OF FAMILY PLATYSCELIDAE 



1 . Pereopods I and II with chelae 2. 



— Pereopods I and II without chelae 4. 



2. Distal process of 5th segment of pereopods I and II with smooth mar- 

 gins; posterior margin of 6th segment bears large pointed tooth. Pere- 

 opods VI seven-segmented. Telson not fused with last urosomite . . 

 5. Amphithyrus Claus. 



