P^ECILASMA FISSA. 109 



shorter than those on the anterior face. This peculiar 

 structure is common to all five posterior cirri. 



Caudal Appendages. — I can only say that they are 

 spinose on their summits. 



Affinities. — This species is allied to P. eburnea in the 

 rudimentary condition of its terga ; in the disc-shaped 

 basal end of its carina ; and in the presence in some 

 specimens, of a fissure-like line on the scuta parallel to 

 their occludent margins. Its affinity, however, is closer 

 to P. fssa, as is more especially shown by the remark- 

 able arrangement of the spines on the five posterior cirri. 



4. P^CILASMA FISSA. PI. II, Fig. 4. 



P. valvis 7; scuto utroque e duobus juxtapositis segmentis 

 formato ; segmento altero intus dentato : tergis brevibus, 

 ier aut quater carina latioribus: carina termino basali in 

 discum parvum angustum infossum producto. 



Valves 7 ; each scutum being formed of two closely 

 approximate segments; of which one is internally toothed: 

 terga short, three or four times as wide as the carina: 

 carina with the basal end produced into a small, narrow, 

 imbedded disc. 



Spines on the segments of the posterior cirri arranged 

 in single transverse rows. 



Philippine Archipelago; Island of Bohol; parasitic on a spinose crab, 

 found under a stone at low water ; single specimen, in Mus., Cuming. 



General Appearance. — Capitulum gibbous, broadly 

 oval, nearly a quarter of an inch long. Valves white, 

 smooth, moderately thick, marked by the lines of growth. 

 The occludent segments of the scuta, and nearly the 

 whole of the terga, and the whole of the carina, enveloped 

 in lemon-yellow membrane, tinged with orange, but the 

 specimen had long been kept dry. 



Scuta formed of two, apparently always separate, 

 segments, closely united, so that externally their separa- 



