102 PJ3CILASMA K.EMPIERI. 



the upper part, with a row of teeth on the crest. The 

 mandibles have four teeth., with the inferior point narrow 

 and spine-like, or rudimentary and absent. The maxillce 

 have, under the two or three upper great spines, a deep 

 notch itself bearing spines ; beneath this, the lower part 

 is straight and considerably prominent, PI. X, fig. 15. 

 Outer maxillae are covered on their inner sides con- 

 tinuously with spines. 



Cirri. — The first pair is sometimes seated very distant 

 from the second. The arrangement of the spines on the 

 posterior cirri varies, to an unusual degree within the 

 limits of the same genus. We have either the ordinary 

 structure of anterior pairs, with single fine intermediate 

 spines (as in P. Kampferi and aurantid), or we have the 

 pairs increased by one or two additional longitudinal 

 lateral rows, as in P. eburnea ; or we have the front 

 spines forming a single transverse row, as in P. crassa 

 and P.Jissa, PL X, fig. 29, a. The segments in none 

 of the species are protuberant; the anterior ramus of 

 the second cirrus does not seem to be thicker than the 

 posterior ramus, as is usually the case. The rami of the 

 second, and of most of the other cirri, are unequal in 

 length, — the anterior ramus, contrary to the ordinary 

 rule, being longer in P. eburnea, P.jissa, and P. crassa, 

 than the posterior ramus by several segments ; I have 

 hitherto observed this inequality only in the sessile genus 

 Chthamalus. 



The Caudal Appendages are small, uniarticulate, and 

 always furnished with bristles. 



Distribution. — Four out of the five species live attached to Crustacea in 

 the European and Eastern warmer temperate and tropical oceans ; the fifth 

 species was found attached to the dead spines of an Echinus, off New 

 Guinea. It is probable that several more species will be hereafter discovered. 



1. P^ECILASMA ICeMPEERI. PI. II, Fig. 1. 



P. valvis 5; camice basi truncatd et cristatd : scuto- 

 rum dentibus intemis umbonalibus fortibus : tergo- 



