100 GENUS — P.ECILASMA. 



second cirrus not thicker than the posterior ramus ; 

 caudal appendages uniarticulate, spinose. 



Generally attached to Crustacea. 



I have already given my reasons for instituting and 

 separating this genus from Lepas ; as far as the capi- 

 tulum is concerned, the differences between these genera 

 certainly appear trivial ; they consist in the carina not 

 extending up between the terga, and in the lower end 

 being either truncated, or produced into an imbedded 

 disc : the terga have a single occludent margin. The 

 included animal's body differs in more important re- 

 spects ; for both mandibles and maxillae are very dis- 

 tinct ; the cirri of some of the species also differ ; and 

 the caudal appendages are here always spinose : there 

 are no filamentary appendages : and lastly, the habits are 

 different. 



The genus may be divided into two sections, firstly, 

 P. Kcempferi and P. aurantia, which have their carina? 

 basally truncated, the basal angles of their terga cut 

 off, and the anterior rami of their second cirri shorter 

 than the posterior rami; and, secondly, P. crassa, P.fissa, 

 and P. eburnea, which in these several respects are other- 

 wise characterised. The P. eburnea, however, differs 

 rather more from P. crassa and P. Jissa, than these two 

 do from each other ; but certainly not enough to allow of 

 the retention of Mr. Hinds' genus of Trilasmis. P. crassa, 

 in an especial degree, connects together all the forms. 



General dyjjjearance. — Capitulum oval, more or less 

 produced, flat or gibbous ; formed of three, five, or seven 

 approximate valves ; the lesser number arising from the 

 abortion of the terga, and the greater number from the 

 scuta being divided into two segments. Valves mode- 

 rately thick, either white or reddish, smooth or striated, 

 and sometimes partly covered by membrane, bearing 

 minute spines. Scuta oval, of varying proportions ; the 

 basal margin is generally narrow, and blends into the 



